Engineered-phosphor LED packages and related methods

ABSTRACT

In accordance with certain embodiments, regions of spatially varying wavelength-conversion particle concentration are formed over light-emitting dies.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/166,329, filed Jan. 28, 2017, which is a continuation-in-part of U.S.patent application Ser. No. 13/770,432, filed Feb. 19, 2013, the entiredisclosure of each of which is incorporated by reference herein.

FIELD OF THE INVENTION

In various embodiments, the present invention generally relates tolight-emitting diodes (LEDs) and, in particular, to LED dies packagedwith engineered phosphor layers.

BACKGROUND

An increasing number of light fixtures utilize LEDs as light sources dueto their lower energy consumption, smaller size, improved robustness,and longer operational lifetime relative to conventional filament-basedlight sources. Conventional LEDs emit quasi-monochromatic radiationranging from infrared through the visible spectrum to ultraviolet.Conventional LEDs emit light at a particular wavelength, ranging from,for example, red to blue or ultraviolet (UV) light. However, forpurposes of general illumination, the relatively narrow spectral widthof light emitted light by LEDs is generally converted to broad-spectrumwhite light.

Traditionally, there are two ways of obtaining white light from LEDs.One approach utilizes two or more LEDs operating at differentwavelengths, where the different wavelengths are chosen such that theircombination appears white to the human eye. For example, one may useLEDs emitting in the red, green, and blue wavelength ranges. Such anarrangement typically requires careful control of the operating currentsof each LED, such that the resulting combination of wavelengths isstable over time and different operating conditions, for exampletemperature. Because the different LEDs may be formed from differentmaterials, different operating parameters may be required for thedifferent LEDs; this complicates the LED circuit design. Furthermore,such systems typically require some form of light combiner, diffuser ormixing chamber, so that the eye sees white light rather than thedistinct colors of each of the different LEDs. Such light-mixing systemstypically add cost and bulk to lighting systems and may reduce theirefficiency.

White light may also be produced in LED-based systems for generalillumination via the utilization of light-conversion materials such asphosphors, sometimes called phosphor-converted LEDs. For example, an LEDcombined with a wavelength-conversion element (WCE) generates whitelight by combining the short-wavelength radiant flux (e.g., blue light)emitted by the semiconductor LED with long-wavelength radiant flux(e.g., yellow light) emitted by, for example one or more phosphorswithin the WCE. The chromaticity (or color), color temperature, andcolor-rendering index are determined by the relative intensities of thecomponent colors. For example, the light color may be adjusted from“warm white” with a correlated color temperature (CCT) of 2700 Kelvin orlower to “cool white” with a CCT of 6500 Kelvin or greater by varyingthe type or amount of phosphor material. White light may also begenerated solely or substantially only by the light emitted by the oneor more phosphor particles within the WCE. A WCE may also be referred toas a phosphor conversion element (PCE) or a phosphor.

PCEs may be positioned in contact with the LED die or positionedapart—that is, remotely from the LED; in this configuration, the PCE iscalled a “remote phosphor.” Both remote-phosphor and contact-phosphorconfigurations produce a non-uniform color distribution as a function ofthe emission angle from the LED-based illumination system, therebyreducing the quality of light and the suitability of the light sourcefor lighting products. Non-uniformity of the angular color distributionfrom phosphor-converted LEDs (PCLED) results from differences in theangular intensity distributions of the LED light and thephosphor-converted light. For example, the LED typically exhibits aLambertian luminous intensity distribution pattern, while emission fromthe phosphor typically exhibits a substantially isotropic luminousintensity distribution. In the case of a phosphor-converted white LED,the blue light emitted from an LED die has a non-isotropic colordistribution (such as a Lambertian distribution) whereas light convertedby a PCE with a yellow emission peak has a substantially isotropic colordistribution. As a consequence, the chromaticity of the combined lightvaries with viewing angle, resulting in a non-uniform color distributionas seen by the human eye. For example, a phosphor-coated blue LED may betypically perceived as being cool white when viewed head-on, but warmwhite when viewed obliquely.

Lighting and illumination systems that include LEDs frequently sufferfrom the angularly dependent color non-uniformity of phosphor-convertedLEDs. In order to mitigate the relatively poor angular color uniformityof conventional phosphor-converted LEDs, such illumination systems oftenrequire additional elements, such as diffusers, mixing chambers, or thelike, to homogenize the color characteristics. Such homogenization oftendegrades the light-intensity distribution pattern, however, resulting inthe need for secondary optics to re-establish the desiredlight-intensity distribution pattern. The addition of these elementstypically requires undesirable additional space or volume, adds cost andexpense, and reduces output efficiency.

Accordingly, there is a need for structures, systems and proceduresenabling LED-based illumination systems to generate uniform colordistribution of light and operate with high extraction efficiency whileutilizing low-cost integration of phosphors with the LEDs.

SUMMARY

In accordance with certain embodiments, the phosphor-containing regionof a light-emitting element (LEE) is engineered such that the lightemitted by the LEE has a desired color distribution. For example,gradients in phosphor-particle concentration that increase or decreaseperpendicular to an emission face of the LEE (and/or parallel to asidewall of the LEE), rather than varying radially with respect to theLEE, may be formed. Moreover, embodiments of the invention enable morecomplicated distributions of phosphor particles within a binder (e.g.,resinous) disposed on the LEE. For example, phosphor particles may bedisposed within multiple distinct regions, separated from each other byat least one region substantially free of phosphor particles.Additionally, multiple different gradients or distributions may beformed by at least partially curing the binder (or curing only a portionof the binder) during the application of a specific settling force(i.e., a force acting to spatially redistribute the phosphor particleswithin the binder), and then performing additional curing during theapplication of a different “non-neutral-gravity”settling force, i.e., asettling force that is not merely gravitational force acting on anuntilted LEE die (such that gravity acts perpendicular to a top emissionface, for example). Exemplary techniques of applying anon-neutral-gravity settling force include (i) tilting the LEE die sothat gravitational force acts along a particular direction with respectto the die (e.g., not perpendicular to the top or bottom faces of thedie), (ii) rotating the die around a fixed axis (e.g., in a centrifuge),(iii) applying an electric field across the binder, and/or (iv) applyingacoustic energy to the binder. Accordingly, embodiments of the inventionfacilitate engineered phosphor distributions that correct LED (or otherLEE) color non-uniformities and/or provide desired light distributions.

In an aspect, embodiments of the invention feature a light-emittingdevice including or consisting essentially of a bare light-emitting die,a binder, and, disposed within the binder, a plurality ofwavelength-conversion particles for absorbing at least a portion oflight emitted from the light-emitting die and emitting converted lighthaving a different wavelength, converted light and unconverted lightemitted by the light-emitting die combining to form substantially whitelight. The die has (i) a top face and a bottom face opposite the topface, at least one of the top or bottom face being configured foremission of light therefrom, and (ii) a sidewall spanning the top andbottom faces. The binder has top and bottom surfaces, at least one ofwhich is substantially parallel to the top face of the die. At least aportion of the binder extends laterally beyond the sidewall of the die,and at least a portion of the binder is disposed over the top face ofthe die. The concentration of the wavelength-conversion particles variesin a direction substantially perpendicular to one of the top or bottomfaces without varying radially toward or away from the die.

Embodiments of the invention include one or more of the followingfeatures in any of a variety of combinations. The concentration of thewavelength-conversion particles may increase in a direction extendingfrom the top face of the die to the bottom face of the die. Theconcentration of the wavelength-conversion particles may decrease in adirection extending from the top face of the die to the bottom face ofthe die. A portion of the binder may extend proximate the sidewall ofthe die below a plane defined by the top face of the die. A portion ofthe binder may be substantially free of wavelength-conversion particles.The light-emitting die may include or consist essentially of alight-emitting diode die. The light-emitting die may include or consistessentially of a GaN-based semiconductor material (e.g., GaN, AlGaN,AlInGaN, InGaN, and/or alloys thereof). The semiconductor material mayinclude In. The light-emitting die may emit blue or ultraviolet light.The wavelength-conversion particles may include or consist essentiallyof phosphor particles. The phosphor particles may include or consistessentially of garnet and a rare-earth element. The divergence of colortemperature of the substantially white light emitted from the device mayvary, over an angular range of 0° to 70°, 75°, or 80°, no more than 0.01(or even no more than 0.005 over an angular range of 10° to 70° or 75°)in terms of Δu′v′ deviation from a spatially weighted averagedchromaticity. The device may include a substrate (i) having at least twoconductive traces thereon and (ii) disposed proximate the bottom face ofthe light-emitting die. A contact pad may be disposed on thelight-emitting die and electrically connected to a conductive trace onthe substrate. The contact pad may be electrically connected to theconductive trace by (i) a wire bond, (ii) a solder joint, (iii) ananisotropic conductive adhesive, and/or (iv) a conductive adhesive. Thesubstrate may include or consist essentially of a leadframe. Thesubstrate may include or consist essentially of a rigid materialselected from the group consisting of Si, SiC, AlN, AlON, sapphire,silicon oxide, SiAlON, SiCAlON, and alloys thereof. At least a portionof the light-emitting die and at least a portion of the substrate may bedisposed within a package. The package may include or consistessentially of a plastic material and/or a ceramic material.

In another aspect, embodiments of the invention feature a light-emittingdevice including or consisting essentially of a bare light-emitting die,a binder, and, disposed within the binder, a plurality ofwavelength-conversion particles for absorbing at least a portion oflight emitted from the light-emitting die and emitting converted lighthaving a different wavelength, converted light and unconverted lightemitted by the light-emitting die combining to form substantially whitelight. The die has (i) a top face and a bottom face opposite the topface, at least one of the top or bottom face being configured foremission of light therefrom, and (ii) a sidewall spanning the top andbottom faces. The binder has top and bottom surfaces, at least one ofwhich is substantially parallel to the top face of the die. At leastpart of the binder extends laterally beyond the sidewall of the die, andat least part of the binder is disposed over the top face of the die. Ina first portion of the binder disposed between the top face of the dieand the top surface of the binder, the concentration of thewavelength-conversion particles increases in a first direction. In asecond portion of the binder disposed between the top face of the dieand the top surface of the binder, the concentration of thewavelength-conversion particles increases in a second directiondifferent from the first direction, the concentration of thewavelength-conversion particles not varying radially toward or away fromthe die.

Embodiments of the invention include one or more of the followingfeatures in any of a variety of combinations. A portion of the bindermay extend proximate the sidewall of the die below a plane defined bythe top face of the die. A portion of the binder may be substantiallyfree of wavelength-conversion particles. The light-emitting die mayinclude or consist essentially of a light-emitting diode die. Thelight-emitting die may include or consist essentially of a GaN-basedsemiconductor material. The semiconductor material may include In. Thelight-emitting die may emit blue or ultraviolet light. Thewavelength-conversion particles may include or consist essentially ofphosphor particles. The phosphor particles may include or consistessentially of garnet and a rare-earth element. Thewavelength-conversion particles may include or consist essentially ofquantum dots. The divergence of color temperature of the substantiallywhite light emitted from the device may vary, over an angular range of0° to 70°, 75°, or 80°, no more than 0.01 (or even no more than 0.005over an angular range of 10° to 70° or) 75° in terms of Δu′v′ deviationfrom a spatially weighted averaged chromaticity.

In yet another aspect, embodiments of the invention feature alight-emitting device including or consisting essentially of a barelight-emitting die, a binder, and, disposed within the binder, aplurality of wavelength-conversion particles for absorbing at least aportion of light emitted from the light-emitting die and emittingconverted light having a different wavelength, converted light andunconverted light emitted by the light-emitting die combining to formsubstantially white light. The die has (i) a top face and a bottom faceopposite the top face, at least one of the top or bottom face beingconfigured for emission of light therefrom, and (ii) a sidewall spanningthe top and bottom faces. The binder has top and bottom surfaces, atleast one of which is substantially parallel to the top face of the die.At least part of the binder extends laterally beyond the sidewall of thedie, and at least part of the binder is disposed over the top face ofthe die. The binder includes a plurality of spatially distinctconversion regions each comprising wavelength-conversion particlestherewithin, the distinct regions being separated from each other by atleast one transmission region of the binder substantially free ofwavelength-conversion particles.

Embodiments of the invention include one or more of the followingfeatures in any of a variety of combinations. At least one conversionregion may be disposed proximate (and may even share an interface with)the top surface of the binder, and at least one conversion region may bedisposed proximate (and may even share an interface with) the bottomsurface of the binder. A portion of the binder may extend proximate thesidewall of the die below a plane defined by the top face of the die.The light-emitting die may include or consist essentially of alight-emitting diode die. The light-emitting die may include or consistessentially of a GaN-based semiconductor material. The semiconductormaterial may include In. The light-emitting die may emit blue orultraviolet light. The wavelength-conversion particles may include orconsist essentially of phosphor particles. The phosphor particles mayinclude or consist essentially of garnet and a rare-earth element. Thewavelength-conversion particles may include or consist essentially ofquantum dots. The divergence of color temperature of the substantiallywhite light emitted from the device may vary, over an angular range of0° to 70°, 75°, or 80°, no more than 0.01 (or even no more than 0.005over an angular range of 10° to 70° or) 75° in terms of Δu′v′ deviationfrom a spatially weighted averaged chromaticity.

In a further aspect, embodiments of the invention feature a method offabricating a phosphor-converted light-emitting element including orconsisting essentially of a bare light-emitting die having (i) a topface and a bottom face opposite the top face, at least one of the top orbottom face being configured for emission of light therefrom, and (ii) asidewall spanning the top and bottom faces. A binder is disposed overthe top face of the die, the binder (i) having top and bottom surfaces,at least one of which is substantially parallel to the top face of thedie, (ii) comprising a portion extending laterally beyond the sidewallof the die, and (iii) having, disposed therewithin, a plurality ofwavelength-conversion particles for absorbing at least a portion oflight emitted from the light-emitting die and emitting converted lighthaving a different wavelength, converted light and unconverted lightemitted by the light-emitting die combining to form substantially whitelight. A non-neutral-gravity settling force is applied to thewavelength-conversion particles, whereby the wavelength-conversionparticles form a predetermined concentration gradient ofwavelength-conversion particles in at least a portion of the binder. Thebinder is at least partially cured to fix the predeterminedconcentration gradient of wavelength-conversion particles in the atleast a portion of the binder.

Embodiments of the invention include one or more of the followingfeatures in any of a variety of combinations. Applying thenon-neutral-gravity settling force may include or consist essentially of(i) tilting the die whereby gravitational force acts along a directionnot perpendicular to the top or bottom faces of the die, (ii) rotatingthe die around a fixed axis, (iii) applying an electric field across thebinder, and/or (iv) applying acoustic energy to the binder. Applying thenon-neutral-gravity settling force may include or consist essentially ofrotating the die around a fixed axis in a centrifuge. Applying thenon-neutral-gravity settling force may include or consist essentially ofapplying acoustic energy to the binder as a standing wave,wavelength-conversion particles being repelled from peaks in thestanding wave and attracted to troughs in the standing wave. The bindermay be at least partially cured while the non-neutral-gravity settlingforce is applied. At least partially curing the binder may include orconsist essentially of (i) partially curing the binder while thenon-neutral-gravity settling force is applied, and, (ii) after thepartial cure, performing additional curing of the binder while or afterapplying a second non-neutral-gravity settling force different from thenon-neutral-gravity settling force. Applying the secondnon-neutral-gravity settling force may include or consist essentially of(i) tilting the die whereby gravitational force acts along a directionnot perpendicular to the top or bottom faces of the die, (ii) rotatingthe die around a fixed axis, (iii) applying an electric field across thebinder, and/or (iv) applying acoustic energy to the binder. After atleast partially curing the binder, the divergence of color temperatureof the substantially white light emitted from the phosphor-convertedlight-emitting element may vary, over an angular range of 0° to 70° or80°, no more than 0.01 (or even no more than 0.005 over an angular rangeof 10° to 70° or 75°) in terms of Δu′v′ deviation from a spatiallyweighted averaged chromaticity. Applying the binder over the top face ofthe die may include or consist essentially of (i) disposing the binderin a mold, and (ii) disposing the die in the mold to at least partiallysurround the die with the binder. The binder may be at least partiallycured while the die is disposed in the mold.

In yet a further aspect, embodiments of the invention feature a methodof fabricating a plurality of phosphor-converted light-emitting elementseach including or consisting essentially of at least one light-emittingdie having (i) a top face and a bottom face opposite the top face, atleast one of the top or bottom face being configured for emission oflight therefrom, and (ii) a sidewall spanning the top and bottom faces.A binder is applied over the top faces of the dies to form a coatedstructure, the binder having, disposed therewithin, a plurality ofwavelength-conversion particles for absorbing at least a portion oflight emitted from the light-emitting dies and emitting converted lighthaving a different wavelength, converted light and unconverted lightemitted by the light-emitting dies combining to form substantially whitelight. A non-neutral-gravity settling force is applied to thewavelength-conversion particles, whereby the wavelength-conversionparticles form predetermined concentration gradients ofwavelength-conversion particles in portions of the binder proximate eachof the dies. The binder is at least partially cured to fix thepredetermined concentration gradients of wavelength-conversion particlesin the portions of the binder. The coated structure is separated into aplurality of coated portions each including or consisting essentially of(i) a portion of the binder comprising a predetermined concentrationgradient of wavelength-conversion particles and (ii) one or morelight-emitting dies.

Embodiments of the invention include one or more of the followingfeatures in any of a variety of combinations. Each coated portion maycontain one light-emitting die. In at least one of the coated portions,the binder (i) may have top and bottom surfaces, at least one of whichis substantially parallel to the top face of the die, and (ii) mayinclude a portion extending laterally beyond the sidewall of the die.One or more light-emitting dies may be disposed in a package beforeapplying the binder over the top faces of the dies. One or morelight-emitting dies may be disposed in a package after (i) applying thebinder over the top faces of the dies, (ii) applying thenon-neutral-gravity settling force to the wavelength-conversionparticles, and (iii) at least partially curing the binder. One or morelight-emitting dies may be disposed on a substrate. The one or morelight-emitting dies may be disposed on the substrate before applying thebinder over the top faces of the dies. The one or more light-emittingdies may be disposed on the substrate after (i) applying the binder overthe top faces of the dies, (ii) applying the non-neutral-gravitysettling force to the wavelength-conversion particles, and (iii) atleast partially curing the binder. The substrate may include or consistessentially of a leadframe. The substrate may be removed from the one ormore light-emitting dies (i.e., the substrate may be removed from thedies or the dies may be removed from the substrate) after at leastpartially curing the binder.

In another aspect, embodiments of the invention feature a light-emittingdevice that includes or consists essentially of a bare light-emittingdie having (i) a top face and a bottom face opposite the top face, atleast one of the top or bottom face being configured for emission oflight therefrom, and (ii) a sidewall spanning the top and bottom faces,a binder having top and bottom surfaces, at least one of which issubstantially parallel to the top face of the die, wherein at least aportion of the binder is disposed over the top face of thelight-emitting die, and disposed within the binder, a plurality ofwavelength-conversion particles for absorbing at least a portion oflight emitted from the light-emitting die and emitting converted lighthaving a different wavelength. Converted light and unconverted lightemitted by the light-emitting die combine to form substantially whitelight. A divergence of color temperature of the substantially whitelight emitted from the light-emitting device varies, over an angularrange of 0° to 70°, no more than 0.01 in terms of a deviation (e.g., aΔu′v′ deviation, where u′ and v′ are chromaticity coordinates on achromaticity diagram) from a spatially weighted averaged chromaticity.The plurality of wavelength-conversion particles includes or consistsessentially of a first plurality of wavelength-conversion particles of afirst type and a second plurality of wavelength-conversion particles ofa second type different from the first type. Throughout the binder, aconcentration of the first plurality of wavelength-conversion particlesrelative to a total concentration of wavelength-conversion particles iswithin 20% of a concentration of the second plurality ofwavelength-conversion particles relative to the total concentration ofwavelength-conversion particles. The total concentration of thewavelength-conversion particles may vary in a direction substantiallyperpendicular to at least one of the top or bottom faces without varyingradially toward or away from the light-emitting die.

Embodiments of the invention include one or more of the followingfeatures in any of a variety of combinations. At least a portion of thebinder may extend laterally beyond the sidewall of the light-emittingdie. The total concentration of the wavelength-conversion particles mayvary substantially linearly in a portion or substantially all of thebinder. The concentration of the first plurality ofwavelength-conversion particles and/or the concentration of the secondplurality of wavelength-conversion particles may vary substantiallylinearly in a portion or substantially all of the binder. The totalconcentration of the wavelength-conversion particles may varysubstantially step-wise linearly in a portion or substantially all ofthe binder. The concentration of the first plurality ofwavelength-conversion particles and/or the concentration of the secondplurality of wavelength-conversion particles may vary substantiallystep-wise linearly in a portion or substantially all of the binder.Throughout the binder, the concentration of the first plurality ofwavelength-conversion particles relative to the total concentration ofwavelength-conversion particles may be within 10%, or even within 5%, ofthe concentration of the second plurality of wavelength-conversionparticles relative to the total concentration of wavelength-conversionparticles. Each of the first plurality of the wavelength-conversionparticles may be coated with a coating material. The coating materialmay have a density greater than a density of the first type ofwavelength-conversion particle. The first type of wavelength-conversionparticle may have a first density, and the second type ofwavelength-conversion particle may have a second density greater thanthe first density. The coating material may have a density less than adensity of the first type of wavelength-conversion particle. The firsttype of wavelength-conversion particle may have a first density, and thesecond type of wavelength-conversion particle may have a second densityless than the first density.

The index of refraction of the coating material may be substantiallyequal to the index of refraction of the binder. The index of refractionof the coating material may be between (i) an index of refraction ofwavelength-conversion particles of the first and/or second types, and(ii) an index of refraction of the binder. The coating material and thebinder may include or consist essentially of the same material. Thecoating material may form a visible and/or detectable interface with thebinder even if the binder and the coating material include or consistessentially of the same material. The coating material and the bindermay include or consist essentially of different materials. The totalconcentration of the wavelength-conversion particles may not varyradially toward or away from the light-emitting die within a planeparallel to the top and/or bottom faces of the light-emitting die. Thefirst type of wavelength-conversion particle may emit light of a firstcolor when excited by blue or ultraviolet radiation (e.g., from thelight-emitting die). The second type of wavelength-conversion particlemay emit light of a second color when excited by blue or ultravioletradiation. The second color may be different from the first color. Thefirst color may be yellow and/or green (i.e., yellow and greencorresponds to yellow/green or yellowish green light), and/or the secondcolor may be red.

The total concentration of the wavelength-conversion particles mayincrease in a direction extending from the top face of thelight-emitting die to the bottom face of the light-emitting die. Thetotal concentration of the wavelength-conversion particles may decreasein a direction extending from the top face of the light-emitting die tothe bottom face of the light-emitting die. A portion of the binder mayextend proximate the sidewall of the light-emitting die below a planedefined by the top face of the light-emitting die. A portion of thebinder may be substantially free of wavelength-conversion particles. Thelight-emitting die may include or consist essentially of alight-emitting diode die. The light-emitting die may include or consistessentially of a GaN-based semiconductor material. The light-emittingdie may emit blue light and/or ultraviolet light. Thewavelength-conversion particles may include or consist essentially ofphosphor particles. The phosphor particles may include or consistessentially of garnet and a rare-earth element. The divergence of colortemperature of the substantially white light emitted from the device mayvary, over an angular range of 0° to 80°, no more than 0.01 in terms ofΔu′v′ deviation from a spatially weighted averaged chromaticity. Thedivergence of color temperature of the substantially white light emittedfrom the device may vary, over an angular range of 10° to 75°, no morethan 0.005 in terms of Δu′v′ deviation from a spatially weightedaveraged chromaticity.

The device may include a substrate (i) having at least two conductivetraces thereon and (ii) disposed proximate the bottom face of thelight-emitting die. A contact pad may be disposed on the light-emittingdie and may be electrically connected to a conductive trace on thesubstrate. The contact pad may be electrically connected to theconductive trace by (i) a wire bond, (ii) a solder joint, (iii) ananisotropic conductive adhesive, and/or (iv) a conductive adhesive. Thesubstrate may include or consist essentially of a leadframe. Thesubstrate may include or consist essentially of a rigid materialselected from the group consisting of Si, SiC, AlN, AlON, sapphire,silicon oxide, SiAlON, SiCAlON, and alloys thereof (e.g., alloysincluding one or more thereof, with or without other materials). Atleast a portion of the light-emitting die and at least a portion of thesubstrate may be disposed in a package. The package may include orconsist essentially of a plastic material and/or a ceramic material. Thefirst type of wavelength-conversion particle may have a first density.The second type of wavelength-conversion particle may have a seconddensity. The second density may be different from the first density. Thefirst type of wavelength-conversion particle may have a first shape. Thesecond type of wavelength-conversion particle may have a second shape.The second shape may be different from the first shape. The first typeof wavelength-conversion particle may have a first radius (or otherdimension such as a width or length). The second type ofwavelength-conversion particle may have a second radius (or otherdimension such as a width or length). The second radius (or otherdimension such as a width or length) may be different from the firstradius (or other dimension such as a width or length). The ratio of thefirst radius and the second radius may be defined by

${\frac{R_{1}}{R_{2}} = \sqrt{\frac{\rho_{p\; 2} - \rho_{f}}{\rho_{p\; 1} - \rho_{f}}}},$where R1 is the first radius, R2 is the second radius, ρ_(p1) is adensity of the first type of wavelength-conversion particle, ρ_(p2) is adensity of the second type of wavelength-conversion particle, and ρ_(f)is a pre-cured density of the binder (i.e., the density of the binderbefore curing).

In yet another aspect, embodiments of the invention feature a method offabricating a light-emitting device including a bare light-emitting diehaving (i) a top face and a bottom face opposite the top face, the topand/or bottom face being configured for emission of light therefrom, and(ii) a sidewall spanning the top and bottom faces. A binder is appliedover the die (e.g., over at least the top surface of the light-emittingdie). Also applied over the die is a plurality of wavelength-conversionparticles for absorbing at least a portion of light emitted from thelight-emitting die and emitting converted light having a differentwavelength. The plurality of wavelength-conversion particles includes orconsists essentially of a first plurality of wavelength-conversionparticles of a first type and a second plurality ofwavelength-conversion particles of a second type different from thefirst type. A settling force is applied to the wavelength-conversionparticles, whereby the wavelength-conversion particles form a spatialdistribution in which, in at least a portion of the binder (or eventhroughout the binder), a concentration of the first plurality ofwavelength-conversion particles relative to a total concentration ofwavelength-conversion particles is within 20% of a concentration of thesecond plurality of wavelength-conversion particles relative to thetotal concentration of wavelength-conversion particles. The binder is atleast partially cured to fix the spatial distribution ofwavelength-conversion particles in the binder.

Embodiments of the invention include one or more of the followingfeatures in any of a variety of combinations. The converted light may besubstantially white light. A divergence of color temperature of thesubstantially white light emitted from the light-emitting device mayvary, over an angular range of 0° to 70°, no more than 0.01 (e.g., interms of a Δu′v′ deviation, where u′ and v′ are chromaticity coordinateson a chromaticity diagram) from a spatially weighted averagedchromaticity. The divergence of color temperature of the substantiallywhite light emitted from the light-emitting device may vary, over anangular range of 0° to 80°, no more than 0.01 from a spatially weightedaveraged chromaticity. The divergence of color temperature of thesubstantially white light emitted from the light-emitting device mayvary, over an angular range of 10° to 75°, no more than 0.005 from aspatially weighted averaged chromaticity. At least a portion of thebinder may extend laterally beyond the sidewall of the light-emittingdie, and/or at least a portion of the binder may be disposed over thetop face of the light-emitting die. The total concentration of thewavelength-conversion particles may vary in a direction substantiallyperpendicular to the top and/or bottom faces without varying radiallytoward or away from the light-emitting die. In at least a portion of thebinder (or even throughout the binder), the concentration of the firstplurality of wavelength-conversion particles relative to the totalconcentration of wavelength-conversion particles may be within 10%, oreven within 5%, of the concentration of the second plurality ofwavelength-conversion particles relative to the total concentration ofwavelength-conversion particles.

The first plurality and/or the second plurality of thewavelength-conversion particles may be coated with one or more coatingmaterials. The first plurality of the wavelength-conversion particlesmay be coated with a first coating material, and the second plurality ofthe wavelength-conversion particles may be coated with a second coatingmaterial different from the first coating material. The first and secondpluralities of the wavelength-conversion particles may each be coatedwith different amounts of the same coating material. Once the firstplurality and/or the second plurality of wavelength-conversion particlesis coated, the first and second pluralities of wavelength-conversionparticles may have approximately the same density.

The coating material may have a density greater than a density of thefirst type of wavelength-conversion particle. The first type ofwavelength-conversion particle may have a first density, and the secondtype of wavelength-conversion particle may have a second density greaterthan the first density. The coating material may have a density lessthan a density of the first type of wavelength-conversion particle. Thefirst type of wavelength-conversion particle may have a first density,and the second type of wavelength-conversion particle may have a seconddensity less than the first density. The index of refraction of thecoating material may be substantially equal to the index of refractionof the binder. The index of refraction of the coating material may bebetween (i) the index of refraction of wavelength-conversion particlesof the first and/or second type, and (ii) the index of refraction of thebinder. The coating material and the binder may include or consistessentially of the same material. The coating material and the bindermay include or consist essentially of different materials. The totalconcentration of the wavelength-conversion particles may not varyradially toward or away from the light-emitting die within a planeparallel to the top and/or bottom faces of the light-emitting die. Thefirst type of wavelength-conversion particle may emit light of a firstcolor (e.g., yellow and/or green) when excited by blue or ultravioletradiation. The second type of wavelength-conversion particle may emitlight of a second color (e.g., red) when excited by blue or ultravioletradiation, the second color being different from the first color.

The total concentration of the wavelength-conversion particles mayincrease in a direction extending from the top face of thelight-emitting die to the bottom face of the light-emitting die. Thetotal concentration of the wavelength-conversion particles may decreasein a direction extending from the top face of the light-emitting die tothe bottom face of the light-emitting die. A portion of the binder mayextend proximate the sidewall of the light-emitting die below a planedefined by the top face of the light-emitting die. A portion of thebinder may be substantially free of wavelength-conversion particles. Thelight-emitting die may include or consist essentially of alight-emitting diode die. The light-emitting die may include or consistessentially of a GaN-based semiconductor material. The light-emittingdie may emit blue light and/or ultraviolet light. Thewavelength-conversion particles may include or consist essentially ofphosphor particles. The phosphor particles may include or consistessentially of garnet and a rare-earth element.

The first and/or second pluralities of wavelength-conversion particlesmay be mixed into the binder before the binder is applied over the die.The first and/or second pluralities of wavelength-conversion particlesmay be applied over the die (e.g., mixed into the binder) after the atleast a portion of the binder is applied over the die. At least aportion of the plurality of wavelength-conversion particles (e.g., allor part of the first plurality of wavelength-conversion particles and/orall or part of the second plurality of wavelength-conversion particles)may be applied over the light-emitting die before the binder is appliedover the light-emitting die. The settling force may include or consistessentially of a neutral gravitational force (e.g., thewavelength-conversion particles may be allowed to settle in at leastpartially uncured binder under the force of gravity in a directionsubstantially perpendicular to the top and/or bottom face of thelight-emitting die). The settling force may include or consistessentially of a non-neutral-gravity settling force. Applying thenon-neutral-gravity settling force may include or consist essentially oftilting the die whereby gravitational force acts along a direction notperpendicular to the top or bottom faces of the light-emitting die.Applying the non-neutral-gravity settling force may include or consistessentially of rotating the light-emitting die (e.g., around a fixedaxis and/or within a centrifuge). Applying the non-neutral-gravitysettling force may include or consist essentially of applying anelectric field across the binder. Applying the non-neutral-gravitysettling force may include or consist essentially of applying acousticenergy to the binder. The acoustic energy may be applied to the binderas a standing wave, wavelength-conversion particles being repelled frompeaks in the standing wave and attracted to troughs in the standingwave. The binder may be at least partially (or even substantially fully)cured while the settling force is applied.

The light-emitting die may be electrically and/or mechanically connectedto a substrate disposed proximate the bottom face of the light-emittingdie. A contact pad on the light-emitting die may be electricallyconnected to a conductive trace on the substrate. The contact pad may beelectrically connected to the conductive trace by (i) a wire bond, (ii)a solder joint, (iii) an anisotropic conductive adhesive, and/or (iv) aconductive adhesive. The substrate may include or consist essentially ofa leadframe. The substrate may include or consist essentially of a rigidmaterial selected from the group consisting of Si, SiC, AlN, AlON,sapphire, silicon oxide, SiAlON, SiCAlON, and alloys thereof. At least aportion of the light-emitting die and at least a portion of thesubstrate may be disposed within a package. The package may include orconsist essentially of a plastic material and/or a ceramic material. Thefirst type of wavelength-conversion particle may have a first density,and the second type of wavelength-conversion particle may have a seconddensity different from the first density. The first type ofwavelength-conversion particle may have a first shape, and the secondtype of wavelength-conversion particle may have a second shape differentfrom the first shape. The first type of wavelength-conversion particlemay have a first radius, and the second type of wavelength-conversionparticle may have a second radius different from the first radius. Theratio of the first radius and the second radius may be defined by

${\frac{R_{1}}{R_{2}} = \sqrt{\frac{\rho_{p\; 2} - \rho_{f}}{\rho_{p\; 1} - \rho_{f}}}},$where R1 is the first radius, R2 is the second radius, ρ_(p1) is adensity of the first type of wavelength-conversion particle, ρ_(p2) is adensity of the second type of wavelength-conversion particle, and ρ_(f)is a pre-cured density of the binder. The light-emitting die may bedisposed on a substrate before the binder is applied over thelight-emitting die. The substrate may be removed from the light-emittingdie after at least partially curing the binder. The total concentrationof the wavelength-conversion particles may vary substantially linearlyin a portion or substantially all of the binder. The concentration ofthe first plurality of wavelength-conversion particles and/or theconcentration of the second plurality of wavelength-conversion particlesmay vary substantially linearly in a portion or substantially all of thebinder. The total concentration of the wavelength-conversion particlesmay vary substantially step-wise linearly in a portion or substantiallyall of the binder. The concentration of the first plurality ofwavelength-conversion particles and/or the concentration of the secondplurality of wavelength-conversion particles may vary substantiallystep-wise linearly in a portion or substantially all of the binder.

These and other objects, along with advantages and features of theinvention, will become more apparent through reference to the followingdescription, the accompanying drawings, and the claims. Furthermore, itis to be understood that the features of the various embodimentsdescribed herein are not mutually exclusive and can exist in variouscombinations and permutations. Reference throughout this specificationto “one example,” “an example,” “one embodiment,” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the example is included in at least one example ofthe present technology. Thus, the occurrences of the phrases “in oneexample,” “in an example,” “one embodiment,” or “an embodiment” invarious places throughout this specification are not necessarily allreferring to the same example. Furthermore, the particular features,structures, routines, steps, or characteristics may be combined in anysuitable manner in one or more examples of the technology. The term“light” broadly connotes any wavelength or wavelength band in theelectromagnetic spectrum, including, without limitation, visible light,ultraviolet radiation, and infrared radiation. Similarly, photometricterms such as “illuminance,” “luminous flux,” and “luminous intensity”extend to and include their radiometric equivalents, such as“irradiance,” “radiant flux,” and “radiant intensity.” As used herein,the term “substantially” means±10%, and in some embodiments, ±5%. Theterm “consists essentially of” means excluding other materials thatcontribute to function, unless otherwise defined herein. Nonetheless,such other materials may be present, collectively or individually, intrace amounts.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIGS. 1A-1F are schematic illustrations of lighting systems inaccordance with various embodiments of the invention;

FIGS. 2A-2H are schematic illustrations of lighting systems inaccordance with various embodiments of the invention;

FIGS. 3A-3B are schematic illustrations of lighting systems inaccordance with various embodiments of the invention;

FIGS. 4A-4D are schematic illustrations of methods of manufacture oflighting systems in accordance with various embodiments of theinvention;

FIGS. 5A-5F are schematic illustrations of methods of manufacture oflighting systems in accordance with various embodiments of theinvention;

FIGS. 6A-6C are schematic illustrations of lighting systems inaccordance with various embodiments of the invention;

FIGS. 7A and 7B are schematic illustrations of methods of manufacture oflighting systems in accordance with various embodiments of theinvention;

FIGS. 8A-8D are schematic illustrations of methods of manufacture oflighting systems in accordance with various embodiments of theinvention;

FIGS. 9A-9C are schematic illustrations of methods of manufacture oflighting systems in accordance with various embodiments of theinvention;

FIGS. 10A, 10B, and 10D are schematic illustrations of methods ofmanufacture of lighting systems in accordance with various embodimentsof the invention;

FIGS. 10C and 10E are schematic illustrations of lighting systems inaccordance with various embodiments of the invention;

FIGS. 11A and 11B are process flows showing methods of manufacture oflighting systems in accordance with various embodiments of theinvention;

FIG. 12A is a schematic illustration of a lighting system in accordancewith various embodiments of the invention;

FIG. 12B is a plot of color characteristics as a function of polar anglein accordance with various embodiments of the invention;

FIGS. 13A, 13B, 13C, 14A, and 14B illustrate methods of manufacture oflighting systems in accordance with various embodiments of theinvention; and

FIG. 15 is a schematic illustration of a lighting system in accordancewith various embodiments of the invention.

DETAILED DESCRIPTION

FIGS. 1A-1D depict exemplary illumination systems 100, 101, 102, and103, respectively, in accordance with embodiments of the presentinvention, although alternative systems with similar functionality arealso within the scope of the present invention. The illumination systemmay include a light-emitting element (LEE) 130 that emitselectromagnetic radiation within a wavelength regime of interest, forexample, visible blue light or radiation in the UV regime, whenactivated by passing a current through the device. LEE 130 may be atleast partially covered by wavelength-conversion material 140 (alsoreferred to herein as a phosphor), PCE, WCE or phosphor element (PE),all of which are utilized synonymously herein unless otherwiseindicated.

Each LEE 130 may be mounted on a leadframe (i.e., a package for LEEsthat features external contacts (e.g., pins or wires) that areelectrically connected, internal to the leadframe, to contact pads onthe LEE), base, or substrate, as identified as 165 and 192 in FIGS. 1Aand 1B respectively; however, this is not a limitation of the presentinvention and in other embodiments LEEs 130 within the scope of thisinvention may be unmounted or packaged, for example as shown in FIG. 1C.FIG. 1C shows an example of a white die 102 that includes or consistsessentially of an LEE 130 and a phosphor 140.

In some embodiments of the present invention, contacts 180, 185 of LEE130 may be electrically coupled and/or attached to conductive traces orconductive elements, as identified as 160 or 190 in FIGS. 1A and 1Brespectively. Contacts 180, 185 of LEE 130 may be electrically coupledand/or attached to conductive traces 160 or 190 using a variety ofmeans; the method of electrical coupling and/or attachment is not alimitation of the present invention. In some embodiments, contacts 180,185 of LEE 130 may be electrically coupled and/or attached to conductivetraces 160 or 190 using a conductive adhesive, a conductive paste, ananisotropic conductive film, or an anisotropic conductive adhesive(ACA), as shown in FIG. 1A. In some embodiments contacts 180, 185 of LEE130 may be electrically coupled and/or attached to conductive traces 160or 190 using wire bonds 191 as shown in FIG. 1B. In some embodiments LEE130 may be attached to conductive traces 160 or 190 using a conductiveadhesive and/or a non-conductive adhesive. In some embodiments contacts180, 185 of LEE 130 may be electrically coupled and/or attached toconductive traces 160 or 190 using a solder process, eutectic solderprocess, wave solder process, or a solder reflow process. In someembodiments LEE 130 may be electrically coupled and/or attached toconductive traces 160 or 190 in a flip-chip orientation, for example asshown in FIGS. 1A and 1D. The method of electrical coupling and/orattachment of contacts 180, 185 to conductive traces 160 or 190 is not alimitation of the present invention.

The structures shown in FIGS. 1A-1C include one LEE 130; however, thisis not a limitation of the present invention and in other embodimentsthe structure may include multiple LEEs 130, as shown in FIG. 1D. FIG.1D shows a structure 103 that includes a substrate 192 over which havebeen formed conductive elements 160 and to which contacts 180 and 185(not shown for clarity) of LEEs 130 have been electrically coupled.Contacts 180 and 185 may be attached using a variety of means, forexample wire bonding, solder, adhesive, and the like. Exemplarystructure 103 includes four LEEs 130; however, this is not a limitationof the present invention and in other embodiments structure 103 mayinclude any number of LEEs 130, e.g., 10 or 20. Structure 103 alsoincludes package contacts 191, 193 to which conductive elements 160 areelectrically coupled and which are typically electrically connected toan external power source.

Substrates 165 and 192 may be composed of a wide range of materials. Insome embodiments substrates 165 and 192 may have relatively low thermalconductivities. In some embodiments substrates 165 and 192 may haverelatively high thermal conductivities. In some embodiments substrates165 and 192 may be flexible, while in others they may be substantiallyrigid. Substrate 165 may include or consist essentially of asemicrystalline or amorphous material, e.g., polyethylene naphthalate(PEN), polyethylene terephthalate (PET), polycarbonate,polyethersulfone, polyester, polyimide, polyethylene, and/or paper.Substrate 165 may include or consist essentially of multiple layers,e.g., a deformable layer over a rigid layer, for example, asemicrystalline or amorphous material, e.g., PEN, PET, polycarbonate,polyethersulfone, polyester, polyimide, polyethylene, and/or paperformed over a rigid substrate comprising, e.g., acrylic, aluminum,steel, and the like. Depending upon the desired application for whichembodiments of the invention are utilized, substrate 165 may besubstantially optically transparent, translucent, or opaque. Forexample, substrate 165 may exhibit a transmittance or a reflectivitygreater than 65% for optical wavelengths ranging between approximately400 nm and approximately 700 nm. In some embodiments substrate 165 mayexhibit a transmittance or a reflectivity of greater than 65% for one ormore wavelengths emitted by LEE 130 and or PCE 140. Substrate 165 mayalso be substantially insulating, and may have an electrical resistivitygreater than approximately 100 ohm-cm, greater than approximately 1×10⁶ohm-cm, or even greater than approximately 1×10¹⁰ ohm-cm. In someembodiments substrates 165 or 192 may include or consist essentially ofmaterials such as fiberglass, FR4, ceramic materials such as siliconcarbide, aluminum nitride, aluminum oxide, combinations of thesematerials, and the like. In some embodiments substrate 165 or 192 mayinclude or consist essentially of a metal, for example a metalleadframe. The material and form of substrates 165 or 192 is not alimitation of the present invention.

Conductive elements 160 and 190 may be formed via conventionaldeposition, photolithography, and etching processes, plating processes,lamination, lamination and patterning, evaporation sputtering, chemicalvapor deposition or the like or may be formed using a variety ofprinting processes. For example, conductive elements 160 and 190 may beformed via screen printing, flexographic printing, ink-jet printing,and/or gravure printing. The method of formation of conductive elements160 and 190 is not a limitation of the present invention. Conductiveelements 160 and 190 may include or consist essentially of a conductiveink, which may include one or more elements such as silver, gold,aluminum, chromium, copper, and/or carbon. Conductive elements 160 and190 may include or consist essentially of a conductive material, whichmay include one or more elements such as silver, gold, aluminum,chromium, copper, and/or carbon. Conductive elements 160 and 190 mayhave a thickness in the range of about 50 nm to about 500 μm; however,the thickness of conductive elements 160 and 190 is not a limitation ofthe present invention. In some embodiments all or a portion ofconductive elements 160 and 190 may be covered or encapsulated. In someembodiments a layer of material, for example insulating material, may beformed over all or a portion of conductive elements 160 and 190. Such amaterial may include or consist essentially of, for example, a sheet ofmaterial such as that used for substrate 165, a printed layer, forexample using screen, ink jet, stencil or other printing techniques, alaminated layer, or the like. Such a layer may include or consistessentially of, for example, an ink, a plastic, a dielectric, an oxide,or the like. The covering material and/or the method by which it isapplied is not a limitation of the present invention.

In one embodiment, conductive traces 160 may be formed so as to have agap between adjacent conductive traces 160, and LEEs 130 areelectrically coupled to conductive traces 160 using conductive adhesive,e.g., an isotropically conductive adhesive and/or an ACA, for example asshown in FIG. 1A. ACAs may be utilized with or without stud bumps andembodiments of the present invention are not limited by the particularmode of operation of the ACA. For example, the ACA may utilize amagnetic field rather than pressure (e.g., the ZTACH ACA available fromSunRay Scientific of Mt. Laurel, N.J., for which a magnetic field isapplied during curing in order to align magnetic conductive particles toform electrically conductive “columns” in the desired conductiondirection). Furthermore, various embodiments utilize one or more otherelectrically conductive adhesives, e.g., isotropically conductiveadhesives, non-conductive adhesives, in addition to or instead of one ormore ACAs.

A wavelength-conversion material 140 is formed over all or a portion ofLEE 130. The wavelength-conversion material may also be referred to as aphosphor or a PCE or PE. As used herein, wavelength-conversion materialor phosphor refers to any material that shifts the wavelengths of lightirradiating it and/or that is fluorescent and/or phosphorescent, isutilized interchangeably with the terms “light-conversion material” or“phosphor,” and may refer to only a powder or particles or to the powderor particles with a binder. In some embodiments, the phosphor includesor consists essentially of a mixture of one or morewavelength-conversion materials and a matrix material. Thewavelength-conversion material is incorporated to shift one or morewavelengths of at least a portion of the light emitted by the lightemitter to other desired wavelengths (which are then emitted from thelarger device alone or color-mixed with another portion of the originallight emitted by the die). A wavelength-conversion material may includeor consist essentially of phosphor powders, quantum dots or the likewithin a transparent matrix. In some embodiments, the matrix may betransparent or translucent. Phosphors are typically available in theform of powders or particles, and in such case may be mixed in binders,e.g., silicone. Phosphors vary in composition, and may include lutetiumaluminum garnet (LuAG or GAL), yttrium aluminum garnet (YAG) or otherphosphors known in the art. GAL, LuAG, YAG and other materials may bedoped with various materials including for example Ce, Eu, etc. Thephosphor may be a plurality of individual phosphors. The specificcomponents and/or formulation of the phosphor and/or matrix material arenot limitations of the present invention.

The binder may also be referred to as an encapsulant or a matrixmaterial. In one embodiment, the binder includes or consists essentiallyof a transparent material, for example a silicone-based material orepoxy, having an index of refraction greater than 1.35. In oneembodiment, the phosphor includes other materials, for example SiO₂,Al₂O₃, fumed silica or fumed alumina, to achieve other properties, forexample to scatter light, to change the viscosity or to reduce settlingof the powder in the binder. An example of the binder material includesmaterials from the ASP series of silicone phenyls manufactured by ShinEtsu, or the Sylgard series manufactured by Dow Corning. In someembodiments, the binder may be transparent to a wavelength of lightemitted by the phosphor and/or by LEE 130.

The illumination system may include a clear or transparent encapsulantmaterial that may contain scattering particles (e.g., titanium oxide,TiO₂) dispersed around LEE 130 to effectively scatter light.Additionally, a phosphor (e.g., a phosphor or fluorescent material) maybe used for converting a portion of the LEE 130 emissions from one setof wavelengths to another.

As utilized herein, the term “light-emitting element” (LEE) refers toany device that emits electromagnetic radiation within a wavelengthregime of interest, for example, visible, infrared or ultravioletregime, when activated, by applying a potential difference across thedevice or passing a current through the device. Examples oflight-emitting elements include solid-state, organic, polymer,phosphor-coated or high-flux LEDs, laser diodes or other similar devicesas would be readily understood. The emitted radiation of an LEE may bevisible, such as red, blue or green, or invisible, such as infrared orultraviolet. An LEE may produce radiation of a spread of wavelengths. AnLEE may feature a phosphorescent or fluorescent material for convertinga portion of its emissions from one set of wavelengths to another. AnLEE may include multiple LEEs, each emitting essentially the same ordifferent wavelengths. In some embodiments, a LEE is an LED that mayfeature a reflector over all or a portion of its surface upon whichelectrical contacts are positioned. The reflector may also be formedover all or a portion of the contacts themselves. In some embodiments,the contacts are themselves reflective. Herein “reflective” is definedas having a reflectivity greater than 65% for a wavelength of lightemitted by the LEE on which the contacts are disposed. In someembodiments a LEE may comprise an electronic device or circuit or apassive device or circuit. In some embodiments a LEE may include orconsist essentially of multiple devices, for example an LED and a Zenerdiode for static electricity protection. One or more non-LEE devicessuch as zener diodes, transient voltage suppressors (TVSs), varistors,etc., may be included to protect the LEEs 130 from damage which may becaused by high voltage events, such as electrostatic discharge (ESD) orlightning strikes.

In an exemplary embodiment, LEE 130 represents a light-emitting elementsuch as an LED or a laser, but other embodiments of the inventionfeature one or more semiconductor dies with different or additionalfunctionality, e.g., processors, sensors, detectors, control elements,and the like. Non-LEE dies may or may not be bonded as described herein,and may have contact geometries differing from those of the LEEs;moreover, they may or may not have semiconductor layers disposed over asubstrate as discussed below. LEE 130 may be composed of one or morelayers, for example semiconductor layers formed over a substrate. Thesubstrate may, for example, include or consist essentially of one ormore semiconductor materials, e.g., silicon, GaAs, InP, GaN, and may bedoped or substantially undoped (e.g., not intentionally doped). In someembodiments, the substrate includes or consists essentially of sapphireor silicon carbide; however, the composition of the substrate is not alimitation of the present invention. The substrate may be substantiallytransparent to a wavelength of light emitted by the LEE 130. For alight-emitting element, the semiconductor layers may include first andsecond doped layers which preferably are doped with opposite polarities(i.e., one n-type doped and the other p-type doped). One or morelight-emitting layers e.g., or one or more quantum wells, may bedisposed between the first and second doped layers. Each of these layersmay include or consist essentially of one or more semiconductormaterials, e.g., silicon, InAs, AlAs, GaAs, InP, AlP, GaP, InSb, GaSb,AlSb, GaN, AlN, InN, and/or mixtures and alloys (e.g., ternary orquaternary, etc. alloys) thereof. In preferred embodiments, LEE 130 isan inorganic, rather than a polymeric or organic, device.

In some embodiments, substantially all or a portion the substrate isremoved prior to or after the bonding of LEE 130 described below. Suchremoval may be performed by, e.g., chemical etching, laser lift-off,mechanical grinding and/or chemical-mechanical polishing or the like. Insome embodiments, all or a portion of the substrate is removed and asecond substrate—e.g., one that is transparent to or reflective of awavelength of light emitted by LEE 130—is attached to the substrate orsemiconductor layers prior to or after the bonding of LEE 130 asdescribed below. In some embodiments, the substrate includes or consistsessentially of silicon and all or a portion of the silicon substrate maybe removed prior to or after the bonding of LEE 130 to a conductiveelement or other system. Such removal may be performed by, e.g.,chemical etching, laser lift off, mechanical grinding and/orchemical-mechanical polishing or the like. In some embodiments, thesilicon substrate may be partially removed or not removed.

Electrical contact to LEE 130 may be achieved through contacts 180 and185, which may make contact to the p- and n-layers respectively. LEE 130may optionally feature a mirror or reflective surface formed over all orportions of the semiconductor layers and optionally other portions ofLEE 130. The mirror may act to direct light emitted from the lightemitting layer back towards and out the substrate, particularly in aflip-chip configuration, where LEE 130 is mounted contact-side down.

In some embodiments, the LEE 130 has a square shape, while in otherembodiments LEE 130 has a rectangular shape. In some preferredembodiments, to facilitate bonding) LEE 130 has a shape with a dimensionin one direction that exceeds a dimension in an orthogonal direction(e.g., a rectangular shape), and has an aspect ratio of the orthogonaldirections (length to width, in the case of a rectangular shape) of LEE130 greater than about 1.2:1. In some embodiments, LEE 130 has an aspectratio greater than about 2:1 or greater than 3:1. The shape and aspectratio are not critical to the present invention, however, and LEE 130may have any desired shape.

In different embodiments, LEEs 130 may have different sizes. In someembodiments, LEE 130 has one lateral dimension less than 500 μm.Exemplary sizes of semiconductor die 130 may include about 250 μm byabout 600 μm, about 250 μm by about 400 μm, about 250 μm by about 300μm, or about 225 μm by about 175 μm. In some embodiments, LEE 130includes or consists essentially of a small LED die, also referred to asa “microLED.” A microLED generally has one lateral dimension less thanabout 300 μm. In some embodiments, semiconductor die 300 has one lateraldimension less than about 200 μm or even less than about 100 μm. Forexample, a microLED may have a size of about 150 μm by about 100 μm orabout 150 μm by about 50 μm. In some embodiments, the surface area ofthe top surface of a microLED is less than 50,000 μm² or less than10,000 μm². In some embodiments, LEEs 130 may have one lateral dimensiongreater than 500 μm, or greater than 1000 μm, or greater than 2000 μm.

In some embodiments, an LEE 130 may include a white die comprising anLED that is integrated with a light-conversion material before beingattached to a base or substrate. An exemplary schematic of a white die102 is shown in FIG. 1C. The structure in FIG. 1C includes LEE die 130(e.g., a “bare-die” or “unpackaged” LED die) that is partially coveredor encased in light-conversion material 140. All or portions of contacts180, 185 may be exposed to provide for electrical contact to die 130.

In some embodiments, white die 102 may be formed by forminglight-conversion material 140 over and/or around one or more dies 130and then separating this structure into individual white dies asdescribed in U.S. Provisional Patent Application No. 61/589,908, theentirety of which is hereby incorporated by reference. FIGS. 1A-1D showlight-conversion material 140 having a square or rectangular shape;however, this is not a limitation of the present invention and in otherembodiments light-conversion material 140 has a hemispherical orsubstantially hemispherical shape, a parabolic or substantiallyparabolic shape, or any shape. In some embodiments, the shape and otherproperties of light-conversion material 140 are engineered to achievespecific optical characteristics, for example, light-distributionpatterns. FIGS. 1A-1D show substantially the same thickness oflight-conversion material 140 over the top and side walls of LEE 130;however, this is not a limitation of the present invention and in otherembodiments, the thickness of light-conversion material 140 varies overdifferent portions of die 130. White die 102 may be used to produceembodiments of this invention, instead of forming light-conversionmaterial 140 over LEE 130 after attachment of LEE 130 to substrate 165.FIGS. 1A-1D show light-conversion material 140 having sidewalls that areperpendicular or substantially perpendicular to the top surface oflight-conversion material 140; however, this is not a limitation of thepresent invention, and in other embodiments the sidewalls may form anobtuse or oblique angle with the top surface of light-conversionmaterial 140.

FIG. 1E shows another embodiment of the present invention, a lightingsystem 104. Lighting system 104 features multiple LEEs 131, each ofwhich may include or consist essentially of a light emitter or aphosphor-converted light emitter. Multiple LEEs 131 are formed on orattached to a base or fixture 194 (not shown in FIG. 1E or 1F are theLEE contacts and conductive traces and other required or optional lampcomponents, for clarity). As may be seen in FIG. 1E, a lighting systemor luminaire in a basic form may include a fixture or housing 194 andmultiple LEEs 131. Not shown in FIG. 1E or 1F is substrate 165. In someembodiments, lighting system 104 may include a distinct substrate 165while in other embodiments LEEs 131 may be mounted on or over fixture194. Lighting system 106 shown in FIG. 1F is similar to lighting system104 shown in FIG. 1E, with the addition of an optic 132. As shown inFIG. 1F, optic 132 has one optical element associated with each LEE 131;however, this is not a limitation of the present invention and in otherembodiments optic 132 may include a smooth or roughened surface orplate, or multiple LEEs 131 may be associated with each optical element,or multiple optical elements may be associated with each LEE 131.

FIGS. 2A-2H depict several embodiments of the present invention thatfeature an LEE 130 and an overlying PCE 140. In some embodiments, PCE140 comprises one portion while in other embodiments PCE 140 comprisesat least two different portions. These embodiments are not meant to belimiting to the invention, only to highlight various aspects of theinvention. In some embodiments, a first portion 246 contains phosphorparticles or powder, identified as a “phosphor,” and a second portion242 that does not contain phosphor particles or powder, identified as a“binder.” In some embodiments, binder 242 may be transparent to awavelength of light emitted by LEE 130. In some embodiments, binder 242may have an index of refraction between about 1.35 and about 1.75.

As shown in FIGS. 2A-2H, a common aspect of some embodiments of theinvention is that the phosphor layer 246 overhangs and/or wraps aroundthe edges of LEE 130. As shown in FIG. 3A, if there is no overhang,light 310 exiting LEE 130 perpendicularly passes through binder 242 andphosphor 246 and may appear white. Light 320 exiting LEE 130 at a moreshallow angle does not pass through phosphor 246 (it may or may not passthrough binder 242) and appears relatively blue, leading to colortemperature variations with viewing angle. As shown in FIG. 3B, theoverhanging structure of phosphor 246 causes a larger solid angle oflight emitted from LEE 130 to pass through phosphor 246, thus resultingin a relatively smaller color temperature variation with viewing angle.All of these examples include a non-phosphor-containing layer 242;however, this is not a limitation of the present invention, as shown forexample in FIGS. 2G and 2H.

As shown in FIG. 3B, the extent of the solid angle of light emitted byLEE 130 that passes through phosphor 246 is at least partially dependenton the extent of overhang 330, the spacing 340 between the top of LEE130 and the bottom of phosphor layer 246, the height 350 of LEE 130, andthe thickness of phosphor layer 246. It also may depend on the emissionpattern of LEE 130. If LEE 130 is engineered to have a non-Lambertianemission pattern or one that is substantially not Lambertian, then theextent of overhang 330 may be modified (e.g., reduced), and/or spacings340 and/or 350 may be modified (e.g., increased).

LEE 130 may include a substrate over which the active device layers areformed. The structure and composition of such layers are well known tothose skilled in the art. In general, such a layer structure (e.g., foran LED) may include top and bottom cladding layers, one doped n-type andone doped p-type, and one or more active layers (from which most or allof the light is emitted) in between the cladding layers. In someembodiments, the layers collectively may have a thickness in the rangeof about 0.25 μm to about 10 μm. In some embodiments, the substrate istransparent and all or a portion thereof is left attached to the devicelayers. In the case of nitride-based semiconductors (for examplecontaining one more of the elements Al, Ga, In, and nitrogen) thesubstrate is often transparent, and may include or consist essentiallyof, e.g., sapphire, silicon carbide, GaN, or the like. In manyembodiments, the substrates are at least initially thicker than thedevice layers, and may be subsequently thinned, for example to athickness in the range of about 1 μm to about 25 μm, or may even beremoved completely. As discussed above, reducing LEE 130 thickness 350relaxes the need for a larger overhang distance 330. One way to reducethickness 350 is to reduce the device layer thicknesses. Another way isto reduce the substrate thickness or completely or substantiallycompletely remove the substrate after or during fabrication of LEE 130.

FIGS. 4A-4D illustrate one technique of manufacture for the structuresshown in FIGS. 2A-2C. The process starts with formation of one or moreLEEs 130 on a temporary “mold substrate” 410, as shown in FIG. 4A. Thisprocess is similar to that described in U.S. Provisional PatentApplication No. 61/589,908, the entirety of which is incorporated byreference. In one embodiment, a layer of binder material 242 is formedover at least a portion of mold substrate 410 and at least some LEEs130. FIG. 4B shows binder 242 having a height greater than height 350 ofLEE 130, which may lead to a structure similar to that of FIG. 2A, butthis is not a limitation of the present invention and in otherembodiments binder 242 may have a height less than height 350 of LEE130, which may lead to a structure similar to that of FIG. 2E, or mayhave the same as or substantially the same as height 350 of LEE 130,which may lead to a structure similar to that of FIG. 2B.

FIG. 4B shows the structure of FIG. 4A at a later stage of manufacture.In FIG. 4B, binder 242 has been formed over all or some LEEs 130 andmold substrate 410. Binder 242 may be formed in a variety of ways, forexample casting, molding, lamination, and the like. In some embodiments,binder 242 may include or consist essentially of a silicone-basedmaterial, PDMS, epoxy, or the like. One example of a silicone-basedbinder is DOW 0E-6652. After formation of binder 242, binder 242 may becured, for example by application of heat, radiation, or the like. Thetop surface of binder 242 may be above the top surface of LEE 130, asshown in FIG. 4B, or it may be equal to or substantially equal the topsurface of LEE 130, or it may be below the top surface of LEE 130.

FIG. 4C shows the structure of FIG. 4B at a later stage of manufacture.In FIG. 4C, phosphor 246 has been formed over all or a portion of binder242. In some embodiments, phosphor 246 may include or consistessentially of phosphor powders that are formed on or infused into aportion of binder 242. For example, phosphor powders may be formed ordeposited on binder 242 at the stage shown in FIG. 4B, either beforecuring, after a partial cure, or after full curing. In otherembodiments, phosphor powders are mixed with a binder, which may be thesame or different from binder 246, and then formed over binder 246, asshown in FIG. 4C.

FIG. 4D shows the structure of FIG. 4C at a later stage of manufacture.In FIG. 4D, the structure of FIG. 4C has been singulated such that eachportion includes one LEE 130, forming the structure of FIG. 2A, afterremoval from mold substrate 410. However, this is not a limitation ofthe present invention and in other embodiments each portion may includemultiple LEEs 130. In the process described above, singulation, shown inFIG. 4D, is perpendicular to or substantially perpendicular to the topsurface of LEE 130 and/or binder 242 and/or phosphor 246; however, thisis not a limitation of the present invention and in other embodimentssingulation may be performed at an angle to the perpendicular, formingeither an acute or obtuse angle. For example, the structure in FIG. 2Cmay be formed using an angled singulation method. In other embodiments,angled sidewalls may be formed using a molding or casting method, asdetailed subsequently. FIGS. 2A-2H show all sidewalls of phosphor 140 asbeing straight; however, this is not a limitation of the presentinvention, and in other embodiments the sidewalls of phosphor 140 may becurved or made up of multiple straight segments or have any shape.

The structure shown in FIGS. 2A-2H and similar structures may also beformed using a mold, as shown in FIG. 5A for the structure shown in FIG.2D. The process starts with a structure like that shown in FIG. 5A.Around each LEE 130 a mold 510 is formed. Mold 510 may be formed on moldsubstrate 410 before or after formation of LEEs 130 on mold substrate410. As shown in FIG. 5A, binder 242 is formed and optionally cured orpartially cured in mold 510.

FIG. 5B shows the structure of FIG. 5A at a later stage of manufacture.In FIG. 5B, phosphor 246 has been formed over all or portions of binder242 and mold 510, followed by curing and singulation of phosphor 246.Removal from mold 510 and mold substrate 410 results in the structureshown in FIG. 2D.

FIGS. 5C-5F show examples of other molds 510; however, the shape of mold510 is not a limitation of the present invention, and in otherembodiments other structures and shapes may be used for mold 510. Thestructures and description above include one binder layer 242 and onephosphor layer 246; however, this is not a limitation of the presentinvention, and in other embodiments more than one layer of each type maybe present, or one type of layer may be absent. For example, in someembodiments binder 242 may be absent and the material surrounding orpartially surrounding LED 130 may include or consist essentially ofphosphor 246. In some embodiments, the material surrounding or partiallysurrounding LED 130 includes or consists essentially of multiple layersof phosphors 246. In some aspects of this embodiment, each of the layersmay have a different concentration of phosphor particles. In someaspects of this embodiment, each of the layers may have a differentcomposition or type of phosphor particles. In some aspects of thisembodiment, each of the layers may have multiple different types ofphosphor particles. In another embodiment, LEEs 130 may be temporarilyattached to mold substrate 410 and flipped over and mated with mold 510into which binder 242 and/or phosphor 246 were previously formed.

In some embodiments of the present invention, improved color temperatureuniformity is achieved by varying the spatial concentration of thephosphor particles in the PCE. Methods for changing the phosphorconcentration by using multiple layers, each of which has a differentphosphor particle concentration, are discussed above. However, thisinvention is not limited to this technique for varying the concentrationof phosphor particles in the PCE, and in other embodiments the phosphorconcentration may be varied by other means, for example by usingsettling of the phosphor powders in the binder, by using differentialcuring of the binder and by other means. Various means for engineeringthe phosphor concentration will be discussed in detail subsequently.

As discussed previously, the emission from a typical LED is Lambertian,while that from the PCE is typically isotropic. One aspect ofembodiments of this invention is the engineering of the phosphorparticle concentration within the PCE to make the intensity of lightemitted by the PCE similar to, the same as, or substantially the same asthat of the LED. In one embodiment of the present invention, this isachieved by engineering the concentration of phosphor particles suchthat there is a relatively lower concentration near the bottom comparedto the top, as shown in FIGS. 6A-6C. FIGS. 6A and 6B show structures inwhich the concentration of phosphor particles varies within one phosphorlayer or the entirety of PCE 140. In FIGS. 6A and 6B the variation inconcentration of phosphor particles is represented by shading, wheredarker shading represents a higher concentration of phosphor particles.FIG. 6C shows a structure in which the concentration of phosphorparticles 630 is varied by forming multiple phosphor layers 242, 242′,and 242″ within PCE 140. While the variation in concentration ofphosphor particles in FIGS. 6A-6C is shown as larger at the top andsmaller at the bottom, this is not a limitation of the present inventionand in other embodiments the phosphor gradient may be reversed, or maybe in any direction.

In some embodiments, the structure shown in FIG. 6C may be manufacturedas discussed above, for example with reference to FIGS. 2A-5F. In someembodiments, settling of the phosphor particles in the binder may beemployed to produce an engineered gradient in phosphor particlecomposition. Phosphor particles typically have a density in the range ofabout 2 gm/cm³ to about 8 gm/cm³, while the binders into which thephosphor particles are mixed, for example silicone binders, have adensity in the range of about 0.5 gm/cm³ to about 2 gm/cm³. Because ofthe relatively significant difference in density between the phosphorparticles and the binder, the phosphor particles will settle under theinfluence of gravity or another accelerating force. The rate of settlingmay be affected or controlled by a number of different parameters, forexample the difference in density of the phosphor particles and binder,the viscosity of the binder, the acceleration force (relatively fixedfor gravitational force on Earth), the radius of the phosphor particles,etc. Additional factors may also affect settling, for exampletemperature, which may change the binder viscosity. The binder viscositymay also be changed by use of additives, for example the phosphorparticles or other additives such as fumed silica, fumed alumina, TiO₂,or the like. The settling direction may be varied by orienting thestructure with respect to the gravitational (or other) applied force.Other forces may be applied to the structure to complement and/orcounteract the force of gravity, for example by putting the structure ina centrifuge or other such system. Of course the gravitational force mayalso be changed by changing the elevation of the system above theEarth's surface or performing the fabrication in zero gravity (e.g., inouter space) or on another planetary body with a different gravitationalforce.

Stoke's law provides an expression for the settling velocity of aparticle under the effect of gravity:

$v_{s} = {\frac{2}{9}\frac{\left( {\rho_{p} - \rho_{f}} \right)}{\mu}{gR}^{2}}$where ν_(s) is the settling velocity, g is gravitational acceleration,ρ_(p) is the mass density of the particle, ρ_(f) is the mass density ofthe fluid, R is the radius of the particle, and μ is the dynamicviscosity of the fluid. While this equation assumes spherical, smoothand non-interacting particles, which may not be the case in allsituations, it provides guidance for the use of settling to engineer aspecific phosphor particle concentration gradient. As Stoke's lawsuggests, decreasing the fluid (binder) viscosity, increasing thedifference in density between the particle and fluid (binder) anddecreasing the particle radius will all result in an increased settlingvelocity. Since the viscosity generally decreases with increasingtemperature, increasing the temperature, for example during the curestep, will also increase the settling velocity. Additives that modifythe binder viscosity, for example, fumed silica, fumed alumina and/orTiO₂, to increase the viscosity, will reduce the settling velocity.

One method for manufacture of this embodiment of the invention startswith LEEs 130 formed on mold substrate 410, as shown in FIG. 7A. Thephosphor particles are mixed with a binder to a desired concentrationand this uncured mixture is put into a mold 510. The mold substrate 410is oriented such that the LEEs 130 are facing down (i.e., toward themold 510), as shown in FIG. 7A, and then is mated with mold 510, asshown in FIG. 7B. Instead of configuring the mixture of phosphorparticles and binder, as well as the process conditions, to achieve auniform or substantially uniform distribution of phosphor particleswithin the PCE, these variables are chosen to result in a specificdesired distribution of phosphor particles within the PCE aftercompletion of the process. In some embodiments, a wait period to allowphosphor particles 630 to settle in the binder is employed beforemating, for example between the steps shown in FIG. 7A and FIG. 7B. Insome embodiments, a wait period to allow phosphor particles 630 tosettle in the binder is employed after mating, that is after the stepshown in FIG. 7B. In some embodiments, settling takes place when thestructure shown in FIG. 7B is heated before or during the process tocure the binder. In some embodiments, the structure shown in FIG. 7B maybe subject to additional acceleration, for example in a centrifuge, toenhance settling. In some embodiments, particles with differentdensities or different radii or both may be used to control the settlingrate. In some embodiments, a combination of these techniques may beused. In some embodiments, additives may be included in the binder tochange the binder viscosity and thus the particle settling velocity.After curing of the binder, mold 510 or mold substrate 410 or both maybe removed and the structure singulated to form the structure shown inFIG. 6A. Achievement of the desired phosphor concentration to achieveuniform or substantially uniform or improved color temperatureuniformity with view angle may be achieved through simulation,experimentation, or a combination of both.

In some embodiments, the concentration of phosphor may increasemonotonically from a first surface of PCE 140 to a second surface of PCE140 opposite the first surface, for example from surface 620 to surface610. In this embodiment, the phosphor concentration is relatively orsubstantially constant in a cut across PCE 140 in a direction parallelto the first or second surface of PCE 140, for example through line A′-Ain FIG. 6A; however, this is not a limitation of the present invention,and in other embodiments the phosphor concentration may vary in a cutacross PCE 140 in a direction parallel to the first or second surface ofPCE 140, for example through line A′-A.

One aspect of embodiments of the present invention is that settling maybe engineered to produce a monotonic as well as a non-monotonic phosphorgradient, and/or the phosphor gradient may be formed in a directiondifferent than that shown by arrow 640 in FIGS. 6A and 6B. In someembodiments, settling may occur in multiple different directions, forexample to form phosphor gradients in multiple directions. In someembodiments, settling may be driven by gravitational and/or centrifugalforce. In some embodiments, settling may be driven by other appliedforces in combination with a gravitational force or by other appliedforces alone. In some embodiments, the resulting phosphor layer may havea smooth or substantially smooth gradient in phosphor particleconcentration in one or more directions. In some embodiments, a smoothgradient may be defined as no step (i.e., abrupt) change in phosphorconcentration in PCE 140 larger than 10% of the maximum phosphorparticle concentration along the gradient. In some embodiments, a smoothgradient may be defined as no step change in phosphor concentration inPCE 140 larger than 5% of the maximum phosphor particle concentrationalong the gradient. In some embodiments, a smooth gradient may bedefined as no step change in phosphor concentration in PCE 140 largerthan 1% of the maximum phosphor particle concentration. In someembodiments, the structure may feature a step-graded structure.

In another embodiment, differential or selective curing is utilized tocreate different structures. For example, a heating plate (or other heatsource) may be applied to one side of mold 510 or mold substrate 410 toselectively cure a layer of the phosphor near the heating plate. Thismay be used to “freeze” some particles in place earlier than others, ormay be used to reduce the viscosity of the binder near the heating plateor both.

In another embodiment, the process in the previous paragraph may only bepartially carried out, that is the binder only partially cured. Uponremoval of the heating plate after the initial partial cure, theorientation of the mold may be optionally changed. The phosphorparticles may settle in a different orientation and then the binderfully cured. This procedure may be repeated many times until a desiredlayer structure is created, as depicted in FIGS. 8A-8D. FIG. 8A shows anLEE 130 on mold substrate 410 that is mated with mold 510 filled withuncured phosphor 140. FIG. 8B shows the structure of FIG. 8A at a laterstage of manufacture, after partial settling of the phosphor particles,producing a layer of relatively higher concentration phosphor particlesat the bottom of mold 510 and partial curing of the phosphor to lock inor freeze this locally higher phosphor particle concentration,identified as 810. The structure is then turned over, as shown in FIG.8C, and the remaining phosphor particles not in the cured binder areallowed to settle again (in a different direction than the previouspartial cure) and the binder fully cured, producing two locally higherphosphor particle concentrations, identified as 810 and 820. Thephosphor particle concentration in region 810 may be greater or lessthan that in region or layer 820. After removal from mold 510 and moldsubstrate 410 and optional singulation, the structure is as shown inFIG. 8D. The structure in FIG. 8D shows layers 810 and 820 having ahigher phosphor particle concentration than the region between layers810 and 820; however, this is not a limitation of the present inventionand in other embodiments, the structure may have more or fewer layers orregions with different phosphor particle concentrations. The processshown in FIGS. 8A-8D features one LEE 130 in mold 510; however, this isnot a limitation of the present invention and in other embodiments mold510 may contain multiple LEEs 130, as shown for example in FIG. 7B. Thestructure shown in FIG. 8D shows three regions of different phosphorconcentrations; however, this is not a limitation of the presentinvention and in other embodiments the structure may have two regions ormore than three regions of different phosphor concentration.

In some embodiments, the phosphor particle concentration may varymonotonically from one side of the LEE or PCE to the other, while inother embodiments the phosphor particle concentration may increase anddecrease with respect to the LEE or PCE. In some embodiments, thephosphor particle concentration within one region or layer (for example810 or 820 in FIG. 8D) may be relatively or substantially homogeneous,while in other embodiments the phosphor particle concentration withinone region or layer may vary. The structures discussed above and shownin the above figures (for example FIGS. 2A-2H, 3A, 3B, 4D, 6A-6C, and8D) show the phosphor particle concentration varying only in thedirection perpendicular to the face comprising the LEE contacts(identified as 610 in FIG. 6A); however, this is not a limitation of thepresent invention, and in other embodiments the phosphor particleconcentration may be varied in other directions or in multipledirections.

FIG. 9A shows an example of a structure in which the phosphor particleconcentration varies in a different direction than that perpendicular tothe face comprising the LED contacts (identified as 610 in FIG. 6A). Asmay be seen in FIG. 9A, the phosphor particle concentration is highestin the upper left and upper right hand corners of PCE 140, and theconcentration of phosphor particles between the upper right and upperleft hand corners is greater than that at the lower portion of PCE 140.

In one embodiment, FIG. 9B shows the structure of FIG. 9A at an earlystage of manufacture. Mold 510 contains LEE 130 and uncured phosphor140. Before full or partial curing of phosphor 140, the mold 510 istilted, as shown in FIG. 9B. The binder is partially cured, for exampleby the application of differential heat or UV radiation and then mold510 is tilted the opposite direction, as shown in FIG. 9C, after whichthe cure is completed. After removal from mold 510 and mold substrate410 and singulation, if necessary, the structure of FIG. 9A is formed.

In another embodiment, the structure of FIG. 9A may be subject to aforce different from that of gravity (for example in a centrifuge ormanufacture in low- or zero-gravity environments such as outer space),or one or more forces in addition to that of gravity. For example,instead of or in addition to tilting, the structure of FIG. 9B may beplaced in a centrifuge to modify the direction of the dominant force onthe structure (which depends on its orientation with respect to the axisof rotation of the centrifuge). Such an approach may be used to makestructures with a monotonic, non-monotonic, or arbitrary phosphorconcentration distribution within PCE 140.

In one embodiment, the phosphor and binder mixture are formed in themold or structure and the phosphor is allowed to settle under an appliedforce, for example nominal Earth gravity. In another embodiment, duringthe settling time one or more other characteristics may be modified, forexample temperature and/or the gravitational force.

In another embodiment, separate phosphor mixtures and binders may beapplied sequentially to the LEE die and cured simultaneously, while inanother embodiment the layers are applied sequentially and cured orpartially cured after each layer application. In one embodiment, awaiting period is included between each mixture application, or betweena mixture application and cure or partial cure, to allow some degrees ofsettling and/or intermixing of the phosphor particles. Such an approachmay be used, for example with the structures shown in FIGS. 4A-4D and5A-5F, with or without advanced mold structures (such as that in FIG. 5Ecomprising a plurality of mold components identified as 510 and 520) toproduce PCEs having monotonic, non-monotonic or arbitrary phosphorconcentration distributions and shapes within the PCE.

While some of the discussions and figures show only one LEE and onemold, or one LEE within one mold, this is not a limitation of thepresent invention and in other embodiments these techniques may be usedto produce multiple phosphor-integrated structures or white diessimultaneously. One preferable aspect of this invention is the use ofthese techniques to produce very large numbers of phosphor-integratedstructures or white dies simultaneously, using batch-type processing atlow cost with desirable optical characteristics and performance.

In some embodiments, the curing is performed by applying microwaveheating; this produces a different thermal profile in an initial stageof cooling, thus allowing a different profile of the phosphor layer. Forexample, in some embodiments upon applying the microwave radiation, thephosphor mixture closest to the LEE die is cured first with one phosphorconcentration. The microwave radiation may then be removed beforecomplete curing of the phosphor mixture, after which curing iscompleted. Upon cooling, settling of the phosphor particles occurs,forming a phosphor density profile around the cured layer, asillustrated in FIG. 10C.

FIG. 10A shows one possible starting point for the manufacture of thestructure shown in FIG. 10C. In the structure shown in FIG. 10A, LEEs130 are formed on mold substrate 410. Mold 510 is used to hold and formphosphor 140. FIG. 10B shows the structure of FIG. 10A at a later stageof manufacture. In FIG. 10B, radiation, for example microwave radiation,has been applied in such a way to selectively or preferentially heat theregion of phosphor 140 surrounding or adjacent to each LEE 130. Thematerial surrounding or adjacent to LEEs 130 may cure or partially cure,forming a first phosphor region 1010. At this point the structure may bethen fully cured, removed from mold 410 and mold substrate 510 andoptionally singulated, resulting in the structure shown in FIG. 10C (inFIG. 10C phosphor region 1010 is represented by a plurality of phosphorparticles 630). In another embodiment, the structure of FIG. 10B issubjected to a wait time, to permit additional phosphor particles tosettle, as shown in FIG. 10D. In FIG. 10D, phosphor 140 now comprisesthree regions, i.e., phosphor 1030 and regions 1010 and 1020, whereregions 1010 and 1020 have a relatively higher phosphor particleconcentration than the regions outside of regions 1010 and 1020, e.g.,region 1030. The structure shown in FIG. 10D may then be cured, removedfrom mold substrate 410 and mold 510 and optionally singulated,resulting in the structure shown in FIG. 10E.

FIG. 11A is a flow chart of one embodiment of the present invention. Instep 1110 the phosphor particles and binder are mixed. In step 1120 thephosphor particle and binder mixture is applied to the LEE. In step 1130the structure is oriented to the applied force, for examplegravitational force, to set the settling direction. In step 1140 thephosphor particles are allowed to settle. In step 1150 the binder iscured. FIG. 11B shows another embodiment, employing a step to modify thesettling characteristics, for example by heating the binder to atemperature high enough to reduce its viscosity from that of ambientconditions, but not high enough to fully cure the binder. As shown inFIG. 11B, the process starts with step 1110, mixing of the phosphorparticles and binder. In step 110 the phosphor particle and bindermixture is applied to the LEE. In step 1130 the structure is oriented tothe applied force, for example gravitational force, to set the settlingdirection. In step 1135 the settling characteristics are modified. Instep 1140 the phosphor particles are allowed to settle. In step 1150 thebinder is cured. In some embodiments, the phosphor particles and binderare applied to the LED in a mold or other confining structure. In someembodiments, the LEE is actually multiple LEEs. In some embodiments, anoptional partial cure of the binder may take place, for example beforesteps 1110, 1120, 1130 or 1140. In some embodiments, the steps may beperformed in a different order, or some steps may be added, or somesteps may be removed. For example, an optional step may includesingulation after step 1150 (curing of the binder). In some embodiments,one or more steps may be repeated. In some embodiments, step 1130 may bemodified to replace the Earth's gravitational force or to modify theEarth's gravitational force (including both direction and/or magnitude)with a replacement or supplemental force, for example a force suppliedusing a centrifuge.

FIG. 12B shows simulations of the divergence of color temperature interms of the Δu′v′ deviation from the spatially weighted averagedchromaticity (0° polar angle is looking directly down on the structureshown in FIG. 12A) as a function of angle for the structure of FIG. 12Awith three different phosphor gradient structures. The variables u′ andv′ are chromaticity coordinates on the CIE 1976 chromaticity diagram.FIG. 12B shows the deviation of the u′v′ color points (i.e., the Δu′v′or u′v′ deviation) as a function of angle from that of the spatiallyweighted average chromaticity. In other words, the average chromaticityover all angles (for example as measured in an integrating sphere) isfirst determined, and then the deviation of the chromaticity at eachangle in units of u′v′ color coordinates is determined. FIG. 12B showsthat deviation plotted as a function of angle. In FIG. 12B, line 1210represents the case where phosphor 140 is homogeneous, line 1220 wherephosphor 140 is linearly graded from the top (surface 620) to the bottom(surface 610) of phosphor 140 (similar to that shown in FIG. 6A) andline 1230 where phosphor 140 is step-graded with 10 equally spaced stepsfrom the top (surface 620) to the bottom (surface 610) of phosphor 140(similar to that shown in FIG. 6C, but with 10 equally spaced steps). Asmay be seen, the color variation (as measured by Δu′v′) as a function ofangle is much lower for the two graded structures than for thehomogeneous structure, except for the value at 60°, which represents thespatially weighted average chromaticity (i.e., the average chromaticityvalue over the entire angular range). The chromaticity deviatessignificantly at both low and high polar angles for the homogeneousphosphor distribution, but is significantly more uniform for both of thegraded structures across the entire polar angle range. There is arelatively small divergence in chromaticity at the highest polar anglesfor the graded structures; however, in many embodiments there isrelatively little optical power at such high polar angles and because ofthis the divergence in color temperature at these very large polarangles is frequently not an issue. In some embodiments, the rate ofgrading may be constant, for example in the linearly graded examplediscussed herein; however, this is not a limitation of the presentinvention, and in other embodiments the rate of grading may changethrough the thickness of the phosphor. In one embodiment, the rate ofgrading may be changed, for example to provide relatively smaller colortemperature variations with angle than may be achieved with a constantrate of grading. In one embodiment, the rate of grading near the topand/or bottom of the phosphor may be changed (i.e., increased ordecreased) to further reduce the color temperature variation at thehigher and lower polar angles, for example in the range of angles ofabout 0° to about 15° and/or about 75° to about 90°. In someembodiments, as shown above, the gradient is in the directionperpendicular to an emitting face 1260 (i.e., the face of the die fromwhich all or a substantial fraction of light is emitted) of LEE 130 andnot in a radial direction toward or away from LEE 130.

In addition to settling, other methods may be used to produce engineeredgradients of phosphor particles within such structures. In someembodiments, some or all of the phosphor particles may be coated orpartially coated with organic ligands. The organic ligands may bedesigned to repel each other, thus promoting a more uniform distributionin the final phosphor structure. In some embodiments, more than one typeof phosphor particle may be used, and each type of phosphor particlecoated or partially coated with a different organic ligand. The organicligands may be designed such that a first organic ligand repels anotherfirst organic ligand, but a first organic ligand attracts a secondorganic ligand. In this case, a first type of phosphor particle may beattracted to a second type of phosphor particle but adjacent first orsecond types of phosphor particles repel each other. In someembodiments, this may promote phosphor uniformity without relying onfumed alumina or silica to prevent phosphor particle clumping.

In some embodiments, the organic ligand may be engineered to beattracted to or repelled by the LEE or one or more materials thereof, orif used, the material of the mold, thus providing another method forengineering a phosphor particle profile. In some embodiments, the moldmay be coated with a material that attracts or repels the organic ligandof the phosphor particle.

In some embodiments, the phosphor particles may be charged while insolution in the uncured binder or its precursors. In this case thephosphor particle distribution may be modified by placing the system inan electric field oriented in the desired direction to produce a desireddistribution. FIG. 13A is a schematic of such a process in whichphosphor particles 630 have a negative charge and experience a force inthe direction of the positive end of an electric field. The directionand strength of the electric field, as well as the viscosity of thebinder and the particle size and charge, may be modified to control thedrift of the phosphor particles in the electric field. The binder maythen be cured or cured in stages with the electric field on or off tofreeze in the desired phosphor particle profile. In some embodiments,the process may be repeated with different electric field directions,partial cures of the binder, or changes in other properties to achieve aspecific monotonic or multi-directional phosphor particle profile. Insome embodiments, an electric field may be generated by situating thesystem between two or more conductive elements 1310, where at least twoof the conductive elements have an opposite charge, as shown in FIG.13B. In some embodiments, an electric field may be generated byapplication of a potential 1320 between two conductive elements 1310. Insome embodiments, the potential may be a DC voltage. In someembodiments, the potential may be an AC voltage. In some embodiments,the conductive elements may include or consist essentially of, forexample, plates or needles. In some embodiments, the shape of one ormore conductive plates may be used to modify the electric field patternand thus induce a phosphor profile that is the same as or similar to theelectric field profile, as shown in FIG. 13C. FIG. 13C shows one flatconductive element or electrode 1310 and one relatively smaller, pointedelectrode or conductive element 1330 that collectively form a modifiedelectric field, as shown by dotted lines 1340. In some embodiments, theelectric field may vary with time during the process or during the cureprocess. In some embodiments, charging of the phosphor particles may beaccomplished by coating or partially coating the phosphor particles withorganic ligands that may be made to accept a charge. In someembodiments, charging of the phosphor particles may be accomplished bytriboelectricity (otherwise known as static electricity). In someembodiments, the phosphor particles may be charged by exposure to lightor other radiation.

In some embodiments, standing acoustic waves may be generated within thephosphor/binder volume, which may provide a driving force for migrationof the phosphor particles towards the standing wave troughs. This may beused to create a monotonic or periodic phosphor particle distribution,as shown in FIGS. 14A and 14B. FIG. 14A shows an embodiment in which astanding acoustic wave 1410 has a crest 1430 within the volume ofphosphor 140, creating a region relatively in the middle of phosphor 140having a high phosphor particle 630 concentration. FIG. 14B shows anembodiment in which standing acoustic wave 1410 has three crests 1430,1430′ and 1430″ within the volume of phosphor 140, creating threeregions of phosphor 140 having a high phosphor particle 630concentrations. In some embodiments, the standing acoustic wave isgenerated using an ultrasonic transducer disposed proximate or incontact with the LEE and/or mold. In some embodiments, two-dimensionalstanding waves may be generated, permitting the manufacture of phosphorparticle distributions that vary in multiple directions. While theexample above shows the crest of standing acoustic wave 1410corresponding to a region of phosphor 140 having a relatively highphosphor particle 630 concentration, this is not a limitation of thepresent invention, and in other embodiments the crest of standingacoustic wave 1410 may correspond to a region of phosphor 140 having arelatively low phosphor particle 630 concentration.

In some embodiments, it may be desirable to use more than one type ofphosphor (e.g., multiple types of phosphor particles) to achieve thedesired optical properties. For example, in one embodiment ayellow-emitting phosphor may be combined with a red-emitting phosphor toachieve a desired color temperature and/or color rendering index (CRI).In some embodiments, more than two different types of phosphors may beutilized.

In some embodiments, it may be desirable to keep the relativeconcentrations of each of the different types of phosphor substantiallythe same within the structure, even when the total phosphor particleconcentration varies as a function of position. That is, at a firstposition within the binder, the total phosphor particle concentrationmay be different from that at a second position within the binder;however, the relative concentrations of the different phosphor types(i.e., the concentration of each phosphor type compared to the totalphosphor particle concentration) may be substantially the same at thefirst and second positions.

In some embodiments, the different types of phosphors may have differentshapes, sizes, and/or densities. These different physicalcharacteristics may result in different settling rates. Furthermore,chemical differences between different types of phosphor particles mayalso result in different settling rates. These effects may result, insome embodiments, in an undesirable variation in the relative localconcentrations of the different phosphor types at different positionswithin the structure. Table 1 below shows properties of a yellow/greenphosphor and a red phosphor particle, both manufactured by MitsubishiChemical Corporation. (The phosphor colors refer to the light emitted bythe phosphor particles when excited by blue or UV radiation.) As may beseen from Table 1, the relatively large difference in density betweenthe two types of particles leads to about a factor of two difference inrelative settling velocity (calculated using the differences in particlediameter and mass density), with the heavier particle having a largersettling velocity. The relative settling velocity was calculated using abinder density of about 1.25 gm/cm³. The expression for relativesettling velocity isRelative v _(s)=(ρ_(p)−ρ_(f))R ²

where ρ_(p) is the mass density of the particle, ρ_(f) is the massdensity of the fluid, and R is the radius of the particle.

TABLE 1 Radius Density Relative Settling Phosphor Color (μm) (gm/cm³)Velocity BG801A Green 8.7 6.7 412 BR102D Red 9.0 3.8 206

The relatively large difference in relative settling velocity may beminimized by adding a coating or shell of a material having a lower massdensity than that of the phosphor particle itself. Table 2 shows therelative settling velocity for a BG801A particle coated with a coatingmaterial (e.g., polymeric binder) having a density of about 1.25. Thetotal thickness of the phosphor particle and binder shell is 17.5 μm,which provides the coated phosphor particle with a relative settlingvelocity of 205, substantially the same as that of the uncoated redphosphor particle in Table 1.

TABLE 2 Radius of Relative Radius of Shell Particle Combined SettlingParticle Thickness and Shell Density Velocity Phosphor (μm) (μm) (μm)(gm/cm³) with Shell BG801A 8.7 8.8 17.5 1.9 205

In an embodiment of the present invention, the difference in relativesettling velocities may be minimized by adding a coating or shell of amaterial having a higher mass density than that of the phosphor particleitself. Table 3 shows the relative settling velocity for a BR102Dparticle coated with a coating material having a density of about 4.9.The total thickness of the phosphor particle and binder shell is about11.5 μm, which provides the coated phosphor particle with a relativesettling velocity of 413, substantially the same as that of the uncoatedgreen phosphor particle in Table 1.

TABLE 3 Radius of Relative Radius of Shell Particle Combined SettlingParticle Thickness and Shell Density Velocity Phosphor (μm) (μm) (μm)(gm/cm³) with Shell BR102D 9.0 2.5 11.5 4.4 413

In some embodiments of the present invention, the relative settlingvelocities of the two different particles (either or both of which maybe coated with one or more coating materials) are within 20% of eachother. In some embodiments of the present invention, the relativesettling velocities of the two different particles are within 10% ofeach other, or even within 5% of each other. In some embodiments, therelative concentrations of the two particles at a given height or depthof the binder, for example in a direction substantially perpendicular toone of the top or bottom faces of light-emitting element 130, are within20% of each other. In some embodiments the relative concentrations ofthe two particles at a given height or depth of the binder, for examplein a direction substantially perpendicular to one of the top or bottomfaces of light-emitting element 130, are within 10% of each other, oreven within 5% of each other.

FIG. 15 shows an example of one embodiment of the invention thatincludes binder 140, light-emitting element 130, and two types ofphosphor particles 1510 and 1520, where phosphor particles 1520 arecoated with a coating 1530.

In some embodiments the coating material includes or consistsessentially of the same material as the binder, while in otherembodiments the coating material is different from the binder material.In some embodiments, the coating material is transparent to a wavelengthof light emitted by the light-emitting element and/or the light emittedby the phosphor particle. In some embodiments, the index of refractionof the coating material may be chosen or engineered to have a specificvalue to optimize one or more optical characteristics of the opticalsystem. For example, in one embodiment the coating may have an index ofrefraction substantially equal to that of the binder in order to reducetotal internal reflection loss between the phosphor particle and thebinder. In one embodiment, the coating may have an index of refractionbetween that of the binder and that of the phosphor particle.

In another embodiment, the radii of the different types of particles(for example particle type 1 and particle type 2) may be varied,resulting in a relationship between the radius of particle 1 and theradius of particle 2 as:

$\frac{R_{1}}{R_{2}} = \sqrt{\frac{\rho_{p\; 2} - \rho_{f}}{\rho_{p\; 1} - \rho_{f}}}$In this manner, the radii of the different types of phosphor particlesmay be selected to provide the phosphor particles with substantiallyequal settling rates within the binder.

While the discussion above is primarily based on blue LEEs andphosphors, that when combined produce white light, the concepts may beused with respect to LEEs emitting at any wavelength and phosphors orwavelength conversion materials with any emission wavelengths that mayin combination or alone be used to produce light of any color.

The terms and expressions employed herein are used as terms andexpressions of description and not of limitation, and there is nointention, in the use of such terms and expressions, of excluding anyequivalents of the features shown and described or portions thereof. Inaddition, having described certain embodiments of the invention, it willbe apparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. Accordingly, thedescribed embodiments are to be considered in all respects as onlyillustrative and not restrictive.

What is claimed is:
 1. A method of fabricating a light-emitting devicecomprising a bare light-emitting die having (i) a top face and a bottomface opposite the top face, at least one of the top or bottom facesbeing configured for emission of light therefrom, and (ii) a sidewallspanning the top and bottom faces, the method comprising: applying overat least the top face of the light-emitting die (i) a binder and (ii) aplurality of wavelength-conversion particles for absorbing at least aportion of light emitted from the light-emitting die and emittingconverted light having a different wavelength, converted light andunconverted light emitted by the light-emitting die combining to formsubstantially white light, the plurality of wavelength-conversionparticles comprising a first plurality of wavelength-conversionparticles of a first type and a second plurality ofwavelength-conversion particles of a second type different from thefirst type; applying a settling force to the wavelength-conversionparticles, whereby each of the first and second plurality ofwavelength-conversion particles form a predetermined concentrationgradient of wavelength-conversion particles in at least a portion of thebinder; and at least partially curing the binder to fix thepredetermined concentration gradient of wavelength-conversion particlesin the at least a portion of the binder to result in a divergence ofcolor temperature of the substantially white light emitted from thelight-emitting device varying, over an angular range of 0° to 70° , nomore than 0.01 in terms of a Δu′v′ deviation from a spatially weightedaveraged chromaticity, where u′ and v′ are chromaticity coordinates on achromaticity diagram.
 2. The method of claim 1, wherein a totalconcentration of the wavelength-conversion particles varies in adirection substantially perpendicular to at least one of the top orbottom faces without varying radially toward or away from thelight-emitting die.
 3. The method of claim 1, whereby thewavelength-conversion particles form a spatial distribution in which,throughout the at least a portion of the binder, a concentration of thefirst plurality of wavelength-conversion particles relative to a totalconcentration of wavelength-conversion particles is within 20% of aconcentration of the second plurality of wavelength-conversion particlesrelative to the total concentration of wavelength-conversion particles.4. The method of claim 1, wherein the divergence of color temperature ofthe substantially white light emitted from the light-emitting devicevaries, over an angular range of 10° to 75°, no more than 0.005 in termsof Δu′v′ deviation from a spatially weighted averaged chromaticity. 5.The method of claim 1, wherein at least a portion of the binder extendslaterally beyond the sidewall of the light-emitting die.
 6. The methodof claim 1, further comprising coating the first plurality of thewavelength-conversion particles with a coating material.
 7. The methodof claim 6, wherein the coating material has a density greater than adensity of the first type of wavelength-conversion particle.
 8. Themethod of claim 7, wherein (i) the first type of wavelength-conversionparticle has a first density, and (ii) the second type ofwavelength-conversion particle has a second density greater than thefirst density.
 9. The method of claim 6, wherein the coating materialhas a density less than a density of the first type ofwavelength-conversion particle.
 10. The method of claim 9, wherein (i)the first type of wavelength-conversion particle has a first density,and (ii) the second type of wavelength-conversion particle has a seconddensity less than the first density.
 11. The method of claim 6, whereinan index of refraction of the coating material is substantially equal toan index of refraction of the binder.
 12. The method of claim 6, whereinan index of refraction of the coating material is between (i) an indexof refraction of wavelength-conversion particles of at least one of thefirst or second types, and (ii) an index of refraction of the binder.13. The method of claim 6, wherein the coating material and the bindercomprise the same material.
 14. The method of claim 6, wherein thecoating material and the binder comprise different materials.
 15. Themethod of claim 1, wherein a total concentration of thewavelength-conversion particles does not vary radially toward or awayfrom the light-emitting die within a plane parallel to at least one ofthe top or bottom faces of the light-emitting die.
 16. The method ofclaim 1, wherein (i) the first type of wavelength-conversion particleemits light of a first color when excited by light emitted by thelight-emitting die, and (ii) the second type of wavelength-conversionparticle emits light of a second color when excited by light emitted bythe light-emitting die, the second color being different from the firstcolor.
 17. The method of claim 16, wherein (i) the first color is atleast one of yellow or green, and (ii) the second color is red.
 18. Themethod of claim 1, wherein a total concentration of thewavelength-conversion particles increases in a direction extending fromthe top face of the light-emitting die to the bottom face of thelight-emitting die.
 19. The method of claim 1, wherein a totalconcentration of the wavelength-conversion particles decreases in adirection extending from the top face of the light-emitting die to thebottom face of the light-emitting die.
 20. The method of claim 1,wherein a portion of the binder extends proximate the sidewall of thelight-emitting die below a plane defined by the top face of thelight-emitting die.
 21. The method of claim 1, wherein thelight-emitting die comprises a light-emitting diode die.
 22. The methodof claim 1, further comprising mixing the plurality ofwavelength-conversion particles into the binder before the binder isapplied over the light-emitting die.
 23. The method of claim 1, whereinat least a portion of the binder is applied over the light-emitting diebefore the plurality of wavelength-conversion particles is applied overthe light-emitting die.
 24. The method of claim 1, wherein at least aportion of the plurality of wavelength-conversion particles is appliedover the light-emitting die before the binder is applied over thelight-emitting die.
 25. The method of claim 1, wherein the settlingforce comprises a neutral gravitational force.
 26. The method of claim1, wherein the settling force comprises a non-neutral-gravity settlingforce.
 27. The method of claim 26, wherein applying thenon-neutral-gravity settling force comprises tilting the die, wherebygravitational force acts along a direction not perpendicular to the topor bottom faces of the light-emitting die.
 28. The method of claim 26,wherein applying the non-neutral-gravity settling force comprisesrotating the light-emitting die.
 29. The method of claim 26, whereinapplying the non-neutral-gravity settling force comprises applying anelectric field across the binder.
 30. The method of claim 26, whereinapplying the non-neutral-gravity settling force comprises applyingacoustic energy to the binder.
 31. The method of claim 30, wherein theacoustic energy is applied to the binder as a standing wave,wavelength-conversion particles being repelled from peaks in thestanding wave and attracted to troughs in the standing wave.
 32. Themethod of claim 1, wherein the binder is at least partially cured whilethe settling force is applied.
 33. The method of claim 1, furthercomprising electrically connecting the light-emitting die to asubstrate.
 34. The method of claim 33, wherein the light-emitting die iselectrically connected to the substrate before the binder is appliedover at least the top face of the light-emitting die.
 35. The method ofclaim 33, wherein the light-emitting die is electrically connected tothe substrate after the binder is applied over at least the top face ofthe light-emitting die.
 36. The method of claim 33, wherein thelight-emitting die is electrically connected to the substrate by atleast one of (i) a wire bond, (ii) a solder joint, (iii) an anisotropicconductive adhesive, or (iv) a conductive adhesive.
 37. The method ofclaim 33, wherein the substrate comprises a flexible material.
 38. Themethod of claim 33, wherein the substrate comprises at least one ofpolyethylene naphthalate, polyethylene terephthalate, polycarbonate,polyethersulfone, polyester, polyimide, polyethylene, or paper.
 39. Themethod of claim 33, wherein electrically connecting the light-emittingdie to the substrate comprises electrically connecting each of at leasttwo contact pads on the light-emitting die to a different conductivetrace on the substrate, the conductive traces comprising at least one ofcopper, aluminum, silver, gold, silver ink, or carbon.
 40. The method ofclaim 1, wherein (i) the first type of wavelength-conversion particlehas a first density, and (ii) the second type of wavelength-conversionparticle has a second density different from the first density.
 41. Themethod of claim 1, wherein (i) the first type of wavelength-conversionparticle has a first shape, and (ii) the second type ofwavelength-conversion particle has a second shape different from thefirst shape.
 42. The method of claim 1, wherein (i) the first type ofwavelength-conversion particle has a first radius, and (ii) the secondtype of wavelength-conversion particle has a second radius differentfrom the first radius.
 43. The method of claim 42, wherein a ratio ofthe first radius and the second radius is defined by$\frac{R_{1}}{R_{2}} = \sqrt{\frac{\rho_{p\; 2} - \rho_{f}}{\rho_{p\; 1} - \rho_{f}}}$wherein R₁ is the first radius, R₂ is the second radius, ρ_(p1) is adensity of the first type of wavelength-conversion particle, ρ_(p2) is adensity of the second type of wavelength-conversion particle, and ρ_(f)is a pre-cured density of the binder.
 44. The method of claim 1, furthercomprising disposing the light-emitting die on a substrate before thebinder is applied over the light-emitting die.
 45. The method of claim44, further comprising removing the substrate from the light-emittingdie after at least partially curing the binder.
 46. The method of claim1, wherein a total concentration of the wavelength-conversion particlesvaries substantially linearly.
 47. The method of claim 1, wherein atleast one of a concentration of the first plurality of thewavelength-conversion particles or a concentration of the secondplurality of the wavelength-conversion particles varies substantiallylinearly.
 48. The method of claim 1, wherein a total concentration ofthe wavelength-conversion particles varies substantially step-wiselinearly.
 49. The method of claim 1, wherein at least one of aconcentration of the first plurality of the wavelength-conversionparticles or a concentration of the second plurality of thewavelength-conversion particles varies substantially step-wise linearly.50. The method of claim 1, wherein a portion of the binder issubstantially free of wavelength-conversion particles after the settlingforce is applied.
 51. The method of claim 50, wherein the portion of thebinder containing wavelength-conversion particles is between thelight-emitting die and the portion of the binder that is substantiallyfree of wavelength-conversion particles.
 52. The method of claim 1,wherein at least partially curing the binder comprises (i) partiallycuring the binder while a non-neutral-gravity settling force is applied,and, (ii) after the partial cure, performing additional curing of thebinder while or after applying a second non-neutral-gravity settlingforce different from the non-neutral-gravity settling force.
 53. Themethod of claim 52, wherein applying the second non-neutral-gravitysettling force comprises at least one of (i) tilting the light-emittingdie whereby gravitational force acts along a direction not perpendicularto the top or bottom faces of the light-emitting die, (ii) rotating thelight-emitting die around a fixed axis, (iii) applying an electric fieldacross the binder, or (iv) applying acoustic energy to the binder. 54.The method of claim 1, wherein applying the binder over the top face ofthe light-emitting die comprises (i) disposing the binder in a mold, and(ii) disposing the light-emitting die in the mold to at least partiallysurround the light-emitting die with the binder.
 55. The method of claim54, wherein the binder is at least partially cured while thelight-emitting die is disposed in the mold.